LC101-200

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LC101 对称二叉树

func dfs(p, q *TreeNode) bool {
    if p == nil && q == nil {
        return true
    }
    if p == nil || q == nil || p.Val != q.Val {
        return false
    }
    return dfs(p.Left, q.Right) && dfs(p.Right, q.Left)
}

func isSymmetric(root *TreeNode) bool {
    if root == nil {
        return true
    }
    return dfs(root.Left, root.Right)
}

LC102 二叉树的层序遍历

var ans [][]int

func dfs(root *TreeNode, dep int) {
    if root == nil {
        return
    }
    if len(ans) == dep {
        ans = append(ans, []int{})
    }
    ans[dep] = append(ans[dep], root.Val)

    if root.Left != nil {
        dfs(root.Left, dep + 1)
    }
    if root.Right != nil {
        dfs(root.Right, dep + 1)
    }
}

func levelOrder(root *TreeNode) [][]int {
    if root == nil {
        return [][]int{}
    }
    ans = make([][]int, 0)
    dfs(root, 0)
    return ans
}

func levelOrder(root *TreeNode) [][]int {
    if root == nil {
        return [][]int{}
    }

    ans := [][]int{}
    q := [] *TreeNode{}
    q = append(q, root)

    for len(q) > 0 {
        s := len(q)
        tmp := []int{}
        for i := 1; i <= s; i ++ {
            t := q[0]
            q = q[1:]
            tmp = append(tmp, t.Val)
            if t.Left != nil {
                q = append(q, t.Left)
            }
            if t.Right != nil {
                q = append(q, t.Right)
            }
        }
        ans = append(ans, tmp)
    }

    return ans
}

LC103 二叉树的锯齿形层序遍历

var ans [][]int

func dfs(root *TreeNode, dep int) {
    if root == nil {
        return
    }
    if len(ans) == dep {
        ans = append(ans, []int{})
    }

    if dep & 1 != 0 {
        ans[dep] = append(append([]int{}, root.Val), ans[dep]...)
    } else {
        ans[dep] = append(ans[dep], root.Val)
    }

    if root.Left != nil {
        dfs(root.Left, dep + 1)
    }
    if root.Right != nil {
        dfs(root.Right, dep + 1)
    }
}

func zigzagLevelOrder(root *TreeNode) [][]int {
    if root == nil {
        return [][]int{}
    }

    ans = make([][]int, 0)
    dfs(root, 0)

    return ans
}

func zigzagLevelOrder(root *TreeNode) [][]int {
    if root == nil {
        return [][]int{}
    }

    ans := [][]int{}
    q := []*TreeNode{}
    q = append(q, root)

    k := 0
    for len(q) > 0 {
        s := len(q)
        tmp := []int{}

        for i := 1; i <= s; i ++ {
            t := q[0]
            q = q[1:]
            tmp = append(tmp, t.Val)
            if t.Left != nil {
                q = append(q, t.Left)
            }
            if t.Right != nil {
                q = append(q, t.Right)
            }
        }
        if k & 1 != 0 {
            i, j := 0, len(tmp) - 1
            for i < j {
                tmp[i], tmp[j] = tmp[j], tmp[i]
                i ++ 
                j --
            }
        }
        ans = append(ans, tmp)
        k ^= 1
    }

    return ans
}

LC104 二叉树的最大深度

func maxDepth(root *TreeNode) int {
    if root == nil {
        return 0
    }
    return max(maxDepth(root.Left), maxDepth(root.Right)) + 1
}

func max(x, y int) int {
    if x > y {
        return x
    }
    return y
}

func maxDepth(root *TreeNode) int {
    if root == nil {
        return 0
    }

    q := []*TreeNode{}
    q = append(q, root)
    dep := 0

    for len(q) > 0 {
        s := len(q)
        for i := 1; i <= s; i ++ {
            t := q[0]
            q = q[1:]
            if t.Left != nil {
                q = append(q, t.Left)
            }
            if t.Right != nil {
                q = append(q, t.Right)
            }
        }
        dep ++ 
    }

    return dep
}

LC105 从前序与中序遍历序列构造二叉树

var pos map[int]int

func build(preorder, inorder []int, pl, pr, il, ir int) *TreeNode {
    if pl > pr {
        return nil
    }
    root := &TreeNode{Val : preorder[pl]}
    k := pos[root.Val]

    if il < k {
        root.Left = build(preorder, inorder, pl + 1, pl + k - il, il, k - 1)
    }
    if k < ir {
        root.Right = build(preorder, inorder, pl + k - il + 1, pr, k + 1, ir)
    }
    
    return root
}

func buildTree(preorder []int, inorder []int) *TreeNode {
    pos = map[int]int{}
    n := len(preorder)
    for i := 0; i < n; i ++ {
        pos[inorder[i]] = i
    }
    return build(preorder, inorder, 0, n - 1, 0, n - 1)
}

LC106 从中序与后序遍历序列构造二叉树

var pos map[int]int

func build(inorder, postorder []int, il, ir, pl, pr int) *TreeNode {
    if il > ir {
        return nil
    }
    root := &TreeNode{Val : postorder[pr]}
    k := pos[root.Val]

    if il < k {
        root.Left = build(inorder, postorder, il, k - 1, pl, pl + k - il - 1)
    }
    if k < ir {
        root.Right = build(inorder, postorder, k + 1, ir, pl + k - il, pr - 1)
    }

    return root
}

func buildTree(inorder []int, postorder []int) *TreeNode {
    pos = map[int]int{}
    n := len(inorder)

    for i := 0; i < n; i ++ {
        pos[inorder[i]] = i
    }

    return build(inorder, postorder, 0, n - 1, 0, n - 1)
}

LC107 二叉树的层序遍历II

var ans [][]int

func dfs(root *TreeNode, dep int) {
    if root == nil {
        return
    }
    if dep == len(ans) {
        ans = append(ans, []int{})
    }
    ans[dep] = append(ans[dep], root.Val)

    if root.Left != nil {
        dfs(root.Left, dep + 1)
    }
    if root.Right != nil {
        dfs(root.Right, dep + 1)
    }
}

func levelOrderBottom(root *TreeNode) [][]int {
    ans = [][]int{}
    if root == nil {
        return [][]int{}
    }
    dfs(root, 0)
    
    l, r := 0, len(ans) - 1
    for l < r {
        ans[l], ans[r] = ans[r], ans[l]
        l ++
        r --
    }

    return ans
}

func levelOrderBottom(root *TreeNode) [][]int {
    if root == nil {
        return [][]int{}
    }
    ans := [][]int{}
    q := []*TreeNode{}
    q = append(q, root)

    for len(q) > 0 {
        s := len(q)
        tmp := []int{}
        for i := 0; i < s; i ++  {
            t := q[0]
            q = q[1 :]
            tmp = append(tmp, t.Val)
            if t.Left != nil {
                q = append(q, t.Left)
            }
            if t.Right != nil {
                q = append(q, t.Right)
            }
        }
        ans = append(ans, tmp)
    }

    l, r := 0, len(ans) - 1
    for l < r {
        ans[l], ans[r] = ans[r], ans[l]
        l ++
        r --
    }

    return ans
}

LC108 将有序数组转换为二叉搜索树

var a []int

func build(l, r int) *TreeNode {
    if l > r {
        return nil
    }
    mid := (l + r) >> 1
    root := &TreeNode{Val : a[mid]}

    root.Left = build(l, mid - 1)
    root.Right = build(mid + 1, r)

    return root
}

func sortedArrayToBST(nums []int) *TreeNode {
    a = nums
    return build(0, len(a) - 1)
}

LC109 有序链表转换为二叉树

func sortedListToBST(head *ListNode) *TreeNode {
    if head == nil {
        return nil
    }

    var slow, fast, preSlow *ListNode
    slow, fast, preSlow = head, head, nil

    for fast != nil && fast.Next != nil {
        preSlow = slow
        slow = slow.Next
        fast = fast.Next.Next
    }

    root := &TreeNode{Val: slow.Val} // slow是中点  将slow作为BST的根节点
    if preSlow != nil {
        preSlow.Next = nil // 建立左子树前，要把 左边链表尾preSlow 指向空
        root.Left = sortedListToBST(head) // head 是 左子树根结点
    }
    root.Right = sortedListToBST(slow.Next) // slow->next 是 右子树根结点

    return root
}

var h *ListNode

func build(l, r int) *TreeNode {
    if l > r {
        return nil
    }

    mid := (l + r) >> 1

    lc := build(l, mid - 1)
    
    root := &TreeNode{Val: h.Val}
    h = h.Next
    root.Left = lc

    root.Right = build(mid + 1, r)

    return root
}

func sortedListToBST(head *ListNode) *TreeNode {
    h = head
    n := 0
    for p := head; p != nil; p = p.Next {
        n ++
    }
    return build(0, n - 1)
}

LC110 平衡二叉树

func getHeight(root *TreeNode) int {
    if root == nil {
        return 0
    }

    lh := getHeight(root.Left)
    if lh == - 1 {
        return -1
    }

    rh := getHeight(root.Right)
    if rh == -1 {
        return -1
    }

    if abs(rh - lh) > 1 {
        return -1
    }
    return max(lh, rh) + 1
} 

func isBalanced(root *TreeNode) bool {
    if root == nil {
        return true
    }

    if getHeight(root) == -1 {
        return false
    }
    return true
}

func abs(x int) int {
    if x < 0 {
        return -x
    }
    return x
}

func max(x, y int) int {
    if x > y {
        return x
    }
    return y
}

LC111 二叉树的最小深度

func minDepth(root *TreeNode) int {
    if root == nil {
        return 0
    }
    if root.Left == nil {
        return 1 + minDepth(root.Right)
    }
    if root.Right == nil {
        return 1 + minDepth(root.Left)
    }
    return min(minDepth(root.Left), minDepth(root.Right)) + 1
}

func min(x, y int) int {
    if x < y {
        return x
    }
    return y
}

LC112 路径总和

func hasPathSum(root *TreeNode, sum int) bool {
    if root == nil {
        return false
    }
    if root.Left == nil && root.Right == nil {
        return sum == root.Val
    }
    return hasPathSum(root.Left, sum - root.Val) || hasPathSum(root.Right, sum - root.Val)
}

LC113 路径总和III

var ans [][]int

func dfs(root *TreeNode, sum int, path []int) {
    if root == nil {
        return
    }
    path = append(path, root.Val)
    sum -= root.Val
    if root.Left == nil && root.Right == nil && sum == 0{
        tmp := make([]int, len(path))
        copy(tmp, path)
        ans = append(ans, tmp)
        return
    }

    if root.Left != nil {
        dfs(root.Left, sum, path)
    }
    if root.Right != nil {
        dfs(root.Right, sum, path)
    }
}
 
func pathSum(root *TreeNode, targetSum int) [][]int {
    if root == nil {
        return [][]int{}
    }
    ans = [][]int{}
    path := []int{}
    dfs(root, targetSum, path)
    return ans
}

LC114 二叉树展开为链表

func flatten(root *TreeNode)  {
    for root != nil {
        p := root.Left
        if p != nil {
            for p.Right != nil {
                p = p.Right
            }
            p.Right = root.Right
            root.Right = root.Left
            root.Left = nil
        }
        root = root.Right
    }
}

LC115 不同的子序列

func numDistinct(s string, t string) int {
    n, m := len(s), len(t)
    if n < m {
        return 0
    }

    s, t = " " + s, " " + t
    f := make([][]int, n + 1)
    for i := 0; i <= n; i ++ {
        f[i] = make([]int, m + 1)
        f[i][0] = 1
    }

    for i := 1; i <= n; i ++ {
        for j := 1; j <= m; j ++ {
            f[i][j] = f[i - 1][j]
            if s[i] == t[j] {
                f[i][j] += f[i - 1][j - 1]
            }
        }
    }

    return f[n][m]
}

LC116 填充每个节点的下一个右侧节点指针

func connect(root *Node) *Node {
    if root == nil {
        return nil
    }
    rt := root
    for root.Left != nil {
        for p := root; p != nil; p = p.Next {
            p.Left.Next = p.Right
            if p.Next != nil {
                p.Right.Next = p.Next.Left
            }
        }
        root = root.Left
    }
    return rt
}

LC117 填充每个节点的下一个右侧节点指针

func connect(root *Node) *Node {
	if root == nil {
        return nil
    }
    rt := root
    for root != nil {
        dummy := &Node{}
        tail := dummy
        for p := root; p != nil; p = p.Next {
            if p.Left != nil {
                tail.Next = p.Left
                tail = tail.Next
            }
            if p.Right != nil {
                tail.Next = p.Right
                tail = tail.Next
            }
        }
        root = dummy.Next
    }
    return rt
}

LC118 杨辉三角

func generate(n int) [][]int {
    f := make([][]int, n)
    for i := 0; i < n; i ++ {
        f[i] = make([]int, i + 1)
        f[i][0], f[i][i] = 1, 1
        for j := 1; j < i; j ++ {
            f[i][j] = f[i - 1][j - 1] + f[i - 1][j]
        }
    }
    return f
}

LC119 杨辉三角II

func getRow(n int) []int {
    f := make([]int, n + 1)
    for i := 0; i <= n; i ++ {
        f[i] = 1
    }
    for i := 0; i <= n; i ++ {
        for j := i - 1; j > 0; j -- {
            f[j] += f[j - 1]
        }
    }
    return f
}

LC120 三角形最小路径和

func minimumTotal(w [][]int) int {
    n := len(w)
    f := make([]int, n + 1)

    for i := n - 1; i >= 0; i -- {
        for j := 0; j <= i; j ++ {
            f[j] = min(f[j], f[j + 1]) + w[i][j]
        }
    }

    return f[0]
}

func minimumTotal(w [][]int) int {
    n := len(w)
    
    for i := n - 2; i >= 0; i -- {
        for j := i; j >= 0; j -- {
            w[i][j] += min(w[i + 1][j], w[i + 1][j + 1])
        }
    }

    return w[0][0]
}

LC121 买卖股票的最佳时机

func maxProfit(prices []int) int {
    ans, low := 0, math.MaxInt32
    for _, x := range prices {
        low = min(low, x)
        ans = max(ans, x - low)
    }
    return ans
}

func maxProfit(prices []int) int {
    n := len(prices)
    f := make([][]int, n)
    for i := 0; i < n; i ++ {
        f[i] = make([]int, 2)
    }

    f[0][0], f[0][1] = 0, -prices[0]
    for i := 1; i < n; i ++ {
        f[i][0] = max(f[i - 1][0], f[i - 1][1] + prices[i])
        f[i][1] = max(f[i - 1][1], -prices[i])
    }

    return f[n - 1][0]
}

LC122 买卖股票的最佳时机II

func maxProfit(prices []int) int {
    n := len(prices)
    f := make([][]int, n)
    for i := 0; i < n; i ++ {
        f[i] = make([]int, 2)
    }

    f[0][0], f[0][1] = 0, -prices[0]
    for i := 1; i < n; i ++ {
        f[i][0] = max(f[i - 1][0], f[i - 1][1] + prices[i])
        f[i][1] = max(f[i - 1][1], f[i - 1][0] - prices[i])
    }

    return f[n - 1][0] 
}

LC123 买卖股票的最佳时机III

func maxProfit(prices []int) int {
    n := len(prices)
    f := make([][]int, 3)
    for i := 0; i < 3; i ++ {
        f[i] = make([]int, 2)
    }
    prices = append([]int{-1}, prices...)

    for j := 0; j <= 2; j ++ {
        f[j][1] = math.MinInt32
    }

    for i := 1; i <= n; i ++ {
        for j := 1; j <= 2; j ++ {
            f[j][0] = max(f[j][0], f[j][1] + prices[i])
            f[j][1] = max(f[j][1], f[j - 1][0] - prices[i])
        }
    }

    return f[2][0]
}

LC124 二叉树中的最大路径和

var ans int

func dfs(root *TreeNode) int {
    if root == nil {
        return 0
    }
    l := max(0, dfs(root.Left))
    r := max(0, dfs(root.Right))
    ans = max(ans, l + root.Val + r)
    return root.Val + max(l, r)
}

func maxPathSum(root *TreeNode) int {
    ans = math.MinInt32
    dfs(root)
    return ans
}

LC125 验证回文串

func check(c byte) bool {
    return c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z' || c >= '0' && c <= '9'
}

func isPalindrome(s string) bool {
    for i, j := 0, len(s) - 1; i < j; i, j = i + 1, j - 1 {
        for i < j && !check(s[i]) {
            i ++
        }
        for i < j && !check(s[j]) {
            j --
        }
        if i < j && strings.ToLower(string(s[i])) != strings.ToLower(string(s[j])) {
            return false
        }
    }
    return true
}

LC126 单词接龙II

class Solution {
public:
    unordered_map dist;
    unordered_set S;
    vector> ans;
    vector path;
    queue q;
    string beginWord, endWord;

    void bfs() {
        q.push(beginWord);
        dist[beginWord] = 0;
        while (!q.empty()) {
            string t = q.front();   q.pop();
            for (int i = 0; i < t.size(); ++ i) {
                string x = t;
                for (char c = 'a'; c <= 'z'; ++ c) {
                    x[i] = c;
                    if (S.count(x) && !dist.count(x)) {
                        dist[x] = dist[t] + 1;
                        if (x == endWord)   break;
                        q.push(x);
                    }
                }
            }
        }
    }

    void dfs(string t) {
        if (t == beginWord) {
            ans.push_back({path.rbegin(), path.rend()});
            return ;
        }

        for (int i = 0; i < t.size(); ++ i) {
            string x = t;
            for (char c = 'a'; c <= 'z'; ++ c) {
                x[i] = c;
                if (dist.count(x) && dist[x] + 1 == dist[t]) {
                    path.push_back(x);
                    dfs(x);
                    path.pop_back();
                }
            }
        }
    }

    vector> findLadders(string beginWord, string endWord, vector& wordList) {
        this->beginWord = beginWord, this->endWord = endWord;
        for (auto& x : wordList)    S.insert(x);
        if (!S.count(endWord))  return {};

        bfs();

        if (!dist.count(endWord))   return {};

        path.push_back(endWord);
        dfs(endWord);

        return ans;
    }
};

LC127 单词接龙

class Solution {
public:
    int ladderLength(string beginWord, string endWord, vector& wordList) {
        queue q;
        unordered_map dist;
        unordered_set S(wordList.begin(), wordList.end());
        if (!S.count(endWord))  return 0;

        dist[beginWord] = 1;
        q.push(beginWord);
        while (!q.empty()) {
            string t = q.front();   q.pop();
            for (int i = 0; i < t.size(); ++ i) {
                string x = t;
                for (char c = 'a'; c <= 'z'; ++ c) {
                    x[i] = c;
                    if (S.count(x) && !dist.count(x)) {
                        dist[x] = dist[t] + 1;
                        if (x == endWord)   return dist[x];
                        q.push(x);
                    }
                }
            }
        }

        return 0;
    }
};

LC128 最长连续序列

func longestConsecutive(nums []int) int {
    S := map[int]bool{}
    for _, x := range nums {
        S[x] = true
    }

    ans := 0
    for _, x := range nums {
        if S[x] && !S[x - 1] {
            delete(S, x)
            y := x
            for S[y + 1] {
                y ++
                delete(S, y)
            }
            ans = max(ans, y - x + 1)
        }
    }

    return ans
}

var f, cnt map[int]int

func find(x int)int {
    if x != f[x] {
        f[x] = find(f[x])
    }
    return f[x]
}

func Union(x, y int) {
    a, b := find(x), find(y)
    if a != b {
        f[a] = b
        cnt[b] += cnt[a]
    }
}

func longestConsecutive(nums []int) int {
    f, cnt = map[int]int{}, map[int]int{}
    for _, x := range nums {
        if _, ok := f[x]; ok {
            continue
        } else {
            f[x], cnt[x] = x, 1
        }

        if _, ok := f[x - 1]; ok {
            Union(x, x - 1)
        }
        if _, ok := f[x + 1]; ok {
            Union(x, x + 1)
        }
    }

    ans := 0
    for _, v := range cnt {
        ans = max(ans, v)
    }

    return ans
}

LC129 求根节点到叶节点数字之和

var ans int

func dfs(root *TreeNode, x int) {
    if root == nil {
        return
    }

    x = x * 10 + root.Val

    if root.Left == nil && root.Right == nil {
        ans += x
        return
    }

    if root.Left != nil {
        dfs(root.Left, x)
    }
    if root.Right != nil {
        dfs(root.Right, x)
    }
}

func sumNumbers(root *TreeNode) int {
    ans = 0
    if root == nil {
        return 0
    }
    dfs(root, 0)
    return ans
}

LC130 被围绕的区域

var (
    dx, dy []int
    n, m int
)

func dfs(g [][]byte, x, y int) {
    g[x][y] = '#'
    for i := 0; i < 4; i ++ {
        a, b := x + dx[i], y + dy[i]
        if a < 0 || a >= n || b < 0 || b >= m || g[a][b] == '#' {
            continue
        }
        if g[a][b] == 'O' {
            dfs(g, a, b)
        }
    }
}

func solve(g [][]byte)  {
    dx, dy = []int{-1, 0, 1, 0}, []int{0, 1, 0, -1}
    n, m = len(g), len(g[0])
    if n == 0 {
        return
    }

    for i := 0; i < n; i ++ {
        if g[i][0] == 'O' {
            dfs(g, i, 0)
        }
        if g[i][m - 1] == 'O' {
            dfs(g, i, m - 1)
        }
    }

    for j := 0; j < m; j ++ {
        if g[0][j] == 'O' {
            dfs(g, 0, j)
        }
        if g[n - 1][j] == 'O' {
            dfs(g, n - 1, j)
        }
    }

    for i := 0; i < n; i ++ {
        for j := 0; j < m; j ++ {
            if g[i][j] == '#' {
                g[i][j] = 'O'
            } else {
                g[i][j] = 'X'
            }
        }
    }
}

var p []int

func find(x int) int {
    if x != p[x] {
        p[x] = find(p[x])
    }
    return p[x]
}

func solve(g [][]byte)  {
    p = []int{}
    dx, dy := []int{-1, 0, 1, 0}, []int{0, 1, 0, -1}
    n, m := len(g), len(g[0])

    for i := 0; i <= n * m; i ++ {
        p = append(p, i)
    }

    for i := 0; i < n; i ++ {
        for j := 0; j < m; j ++ {
            if g[i][j] == 'O' {
                if i == 0 || i == n - 1 || j == 0 || j == m - 1 {
                    p[find(i * m + j)] = find(n * m)
                } else {
                    for k := 0; k < 4; k ++ {
                        a, b := i + dx[k], j + dy[k]
                        if a >= 0 && a < n && b >= 0 && b < m && g[a][b] == 'O' {
                            p[find(i * m + j)] = find(a * m + b)
                        }
                    }
                }
            }
        }
    }

    for i := 0; i < n; i ++ {
        for j := 0; j < m; j ++ {
            if find(i * m + j) == find(n * m) {
                continue
            } else {
                g[i][j] = 'X'
            }
        }
    }
}

LC131 分割回文串

var (
    n int
    path []string
    f [][]bool
    ans [][]string
)

func dfs(s string, i int) {
    if i == n {
        ans = append(ans, append([]string{}, path...))
        return
    }
    for j := i; j < n; j ++ {
        if f[i][j] {
            path = append(path, s[i : j + 1])
            dfs(s, j + 1)
            path = path[ : len(path) - 1]
        }
    }
}

func partition(s string) [][]string {
    n = len(s)
    path = []string{}
    f = make([][]bool, n)
    ans = [][]string{}
    for i := 0; i < n; i ++ {
        f[i] = make([]bool, n)
        for j := 0; j < n; j ++ {
            f[i][j] = true
        }
    }

    for i := n - 1; i >= 0; i -- {
        for j := i + 1; j < n; j ++ {
            f[i][j] = f[i + 1][j - 1] && (s[i] == s[j])
        }
    }

    dfs(s, 0)
    return ans
}

var (
    f [][]bool
    ans [][]string
    path []string
    s string
    n int
)

func dfs(i int) {
    if i == len(s) {
        tmp := make([]string, len(path))
        copy(tmp, path)
        ans = append(ans, tmp)
        return 
    }

    for j := i; j < len(s); j ++ {
        if f[i][j] {
            path = append(path, s[i : j + 1])
            dfs(j + 1)
            path = path[ : len(path) - 1]
        }
    }
}

func partition(_s string) [][]string {
    s = _s
    n = len(s)
    path, ans = []string{}, [][]string{}
    
    f = make([][]bool, n)
    for i := 0; i < n; i ++ {
        f[i] = make([]bool, n)
        for j := 0; j < n; j ++ {
            f[i][j] = false
        }
    }

    for i := 0; i < n; i ++ {
        f[i][i] = true
    }
    
    for len := 2; len <= n; len ++ {
        for i := 0; i + len - 1 < n; i ++ {
            j := i + len - 1
            if len == 2 {
                f[i][j] = s[i] == s[j]
            } else {
                f[i][j] = (s[i] == s[j]) && f[i + 1][j - 1]
            }
        }
    }

    dfs(0)
    return ans
}

var (
    f [][]bool
    ans [][]string
    path []string
    s string
)

func initialize() {
    n := len(s)
    f = make([][]bool, n)
    for i := 0; i < n; i ++ {
        f[i] = make([]bool, n)
    }

    for j := 0; j < n; j ++ {
        for i := 0; i <= j; i ++ {
            if i == j {
                f[i][j] = true
            } else if s[i] == s[j] {
                if i + 1 == j || f[i + 1][j - 1] {
                    f[i][j] = true
                }
            }
        }
    }
}

func dfs(u int) {
    if u == len(s) {
        tmp := make([]string, len(path))
        copy(tmp, path)
        ans = append(ans, tmp)
        return 
    }

    for i := u; i < len(s); i ++ {
        if f[u][i] {
            path = append(path, s[u : i + 1])
            dfs(i + 1)
            path = path[ : len(path) - 1]
        }
    }
}

func partition(_s string) [][]string {
    s = _s
    path, ans = []string{}, [][]string{}
    initialize()
    dfs(0)
    return ans
}

LC132 分割回文串II

func minCut(s string) int {
	n := len(s)
	s = " " + s
	g := make([][]bool, n + 1)
	for i := range g {
		g[i] = make([]bool, n + 1)
	}

	for j := 1; j <= n; j ++ {
		for i := 1; i <= j; i ++ {
			if i == j {
				g[i][j] = true
			} else if s[i] == s[j] {
				g[i][j] = i + 1 == j || g[i + 1][j - 1]
			}
		}
	}

	f := make([]int, n + 1)
	for i := range f {
		f[i] = math.MaxInt32
	}
	f[0] = 0

	for i := 1; i <= n; i ++ {
		for j := 1; j <= i; j ++ {
			if g[j][i] {
				f[i] = min(f[i], f[j - 1] + 1)
			}
		}
	}

	return f[n] - 1
}

func minCut(s string) int {
    n := len(s)
    s = " " + s
    g := make([][]bool, n + 1)
    for i := 0; i < n + 1; i ++ {
        g[i] = make([]bool, n + 1)
        for j := 0; j < n + 1; j ++ {
            g[i][j] = true
        }
    }

    for i := n; i >= 0; i -- {
        for j := i + 1; j < n + 1; j ++ {
            g[i][j] = g[i + 1][j - 1] && (s[i] == s[j])
        }
    }

    f := make([]int, n + 1)
    for i := 0; i < n + 1; i ++ {
        f[i] = math.MaxInt32
    }
    f[0] = 0

    for i := 1; i <= n; i ++ {
        for j := 1; j <= i; j ++ {
            if g[j][i] {
                f[i] = min(f[i], f[j - 1] + 1)
            }
        }
    }

    return f[n] - 1
}

func minCut(s string) int {
	n := len(s)
	s = " " + s
	g := make([][]bool, n + 1)
	for i := range g {
		g[i] = make([]bool, n + 1)
	}
    for i := 1; i <= n; i ++ {
        g[i][i] = true
    }

    for len := 2; len <= n; len ++ {
        for i := 1; i + len - 1 <= n; i ++ {
            j := i + len - 1
            if len == 2 {
                g[i][j] = s[i] == s[j]
            } else {
                g[i][j] = (s[i] == s[j]) && g[i + 1][j - 1]
            }
        }
    }

	f := make([]int, n + 1)
	for i := range f {
		f[i] = math.MaxInt32
	}
	f[0] = 0

	for i := 1; i <= n; i ++ {
		for j := 1; j <= i; j ++ {
			if g[j][i] {
				f[i] = min(f[i], f[j - 1] + 1)
			}
		}
	}

	return f[n] - 1
}

LC133 克隆图

var mp map[*Node]*Node

func dfs(node *Node) {
    mp[node] = &Node{Val: node.Val}
    for i := 0; i < len(node.Neighbors); i ++ {
        ver := node.Neighbors[i]
        if _, ok := mp[ver]; !ok {
            dfs(ver)
        }
    }
}

func cloneGraph(node *Node) *Node {
    if node == nil {
        return nil
    }
    mp = map[*Node]*Node{}
    dfs(node)

    for s, d := range mp {
        for i := 0; i < len(s.Neighbors); i ++ {
            ver := s.Neighbors[i]
            d.Neighbors = append(d.Neighbors, mp[ver])
        }
    }

    return mp[node]
}

LC134 加油站

func canCompleteCircuit(gas []int, cost []int) int {
    i, j, n := 0, 0, len(gas)
    for i < n {
        s := 0
        for j < n {
            k := (i + j) % n
            s += gas[k] - cost[k]
            if s < 0 {
                break
            }
            j ++
        }
        if j == n {
            return i
        }
        i, j = i + j + 1, 0
    }
    return -1
}

func canCompleteCircuit(gas []int, cost []int) int {
    n := len(gas)
    s := make([]int, 2 * n + 1)
    for i := 1; i <= n; i ++ {
        s[i] = gas[i - 1] - cost[i - 1]
        s[i + n] = s[i]
    }
    for i := 1; i <= 2 * n; i ++ {
        s[i] += s[i - 1]
    }

    q := make([]int, 2 * n + 1)
    hh, tt := 0, -1
    for i := 2 * n; i > 0; i -- {
        if hh <= tt && q[hh] > i + n {
            hh ++
        }
        for hh <= tt && s[q[tt]] >= s[i] {
            tt --
        }
        if i <= n && s[q[hh]] - s[i] >= 0 {
            return i % n
        }
        tt ++
        q[tt] = i
    }

    return -1
}

LC135 分发糖果

var (
    n int
    w, f []int
)

func dfs(x int) int {
    if f[x] != -1 {
        return f[x]
    }

    f[x] = 1
    if x > 0 && w[x - 1] < w[x] {
        f[x] = max(f[x], dfs(x - 1) + 1)
    }
    if x + 1 < n && w[x + 1] < w[x] {
        f[x] = max(f[x], dfs(x + 1) + 1)
    }

    return f[x]
}

func candy(ratings []int) int {
    w = ratings
    n = len(w)
    f = make([]int, n)
    for i := 0; i < n; i ++ {
        f[i] = -1
    }

    ans := 0
    for i := 0; i < n; i ++ {
        ans += dfs(i)
    }

    return ans
}

func candy(w []int) int {
    n := len(w)
    l, r := make([]int, n), make([]int, n)
    for i := 0; i < n; i ++ {
        l[i], r[i] = 1, 1
    }

    for i := 1; i < n; i ++ {
        if w[i - 1] < w[i] {
            l[i] = max(l[i], l[i - 1] + 1)
        }
    }

    for i := n - 2; i >= 0; i -- {
        if w[i + 1] < w[i] {
            r[i] = max(r[i], r[i + 1] + 1)
        }
    }

    ans := 0
    for i := 0; i < n; i ++ {
        ans += max(l[i], r[i])
    }

    return ans
}

LC136 只出现一次的数字

func singleNumber(nums []int) int {
    ans := 0
    for _, x := range nums {
        ans ^= x
    }
    return ans
}

LC137 只出现一次的数字II

func singleNumber(nums []int) int {
    ans := int32(0)
    for i := 0; i < 32; i ++ {
        cnt := int32(0)
        for _, x := range nums {
            cnt += int32(x) >> i & 1
        }
        ans |= (cnt % 3) << i
    }
    return int(ans)
}

LC138 随机链表的复制

func copyRandomList(head *Node) *Node {
    if head == nil {
        return nil
    }
    mp := map[*Node]*Node{}
    p := head
    for p != nil {
        mp[p] = &Node{Val: p.Val}
        p = p.Next
    }
    for s, d := range mp {
        if s.Next != nil {
            d.Next = mp[s.Next]
        }
        if s.Random != nil {
            d.Random = mp[s.Random]
        }
    }
    return mp[head]
}

func copyRandomList(head *Node) *Node {
    if head == nil {
        return nil
    }

    p := head
    for p != nil {
        q := &Node{Val: p.Val}
        q.Next = p.Next
        p.Next = q
        p = p.Next.Next
    }

    p = head
    for p != nil {
        if p.Random != nil {
            p.Next.Random = p.Random.Next
        }
        p = p.Next.Next
    }

    dummy := &Node{}
    cur := dummy
    p = head
    for p != nil {
        q := p.Next
        cur.Next = q
        cur = cur.Next
        p.Next = q.Next
        p = p.Next
    }

    return dummy.Next
}

LC139 单词拆分

func wordBreak(s string, wordDict []string) bool {
    const base = 13331

    S := map[uint64]bool{}
    for _, word := range wordDict {
        var x uint64 = 0
        for _, c := range word {
            x = x * base + uint64(c)
        }
        S[x] = true
    }

    n := len(s)
    s = " " + s
    f := make([]bool, n + 1)
    f[0] = true

    for i := 1; i <= n; i ++ {
        for j := 1; j <= i; j ++ {
            var x uint64 = 0
            for k := j; k <= i; k ++ {
                x = x * base + uint64(s[k])
            }
            if f[j - 1] && S[x] {
                f[i] = true
            }
        }
    }

    return f[n]
}

func wordBreak(s string, wordDict []string) bool {
    const base = 13331

    S := map[uint64]bool{}
    for _, word := range wordDict {
        var x uint64 = 0
        for _, c := range word {
            x = x * base + uint64(c)
        }
        S[x] = true
    }

    n := len(s)
    s = " " + s
    f := make([]bool, n + 1)
    f[0] = true

    for i := 0; i < n; i ++ {
        if f[i] {
            var x uint64 = 0
            for j := i + 1; j < n + 1; j ++ {
                x = x * base + uint64(s[j])
                if _, ok := S[x]; ok {
                    f[j] = true
                }
            }
        }
    }

    return f[n]
}

LC140 单词拆分II

var (
    f   []bool
    ans []string
    S   map[string]bool
    s   string
    n   int
)

func dfs(i int, path string) {
    if i == 0 {
        path = path[1:] // 去掉最前面开头的那个空格
        ans = append(ans, path)
        return
    }

    for j := i; j > 0; j -- {
        if f[j - 1] && S[s[j : i + 1]] {
            dfs(j - 1, " " + s[j : i + 1] + path)
        }
    }
}

func wordBreak(_s string, wordDict []string) []string {
    ans = []string{}
    n = len(_s)
    s = " " + _s
    S = make(map[string]bool)
    for _, x := range wordDict {
        S[x] = true
    }

    f = make([]bool, n + 1)
    f[0] = true
    for i := 1; i <= n; i ++ {   // 从前往后预处理出f[]数组
        for j := 1; j <= i; j ++ {
            if f[j - 1] && S[s[j : i + 1]] {
                f[i] = true
                break
            }
        }
    }

    dfs(n, "")
    return ans
}

var (
    f   []bool
    ans []string
    S   map[string]bool
    s   string
    n   int
)

func dfs(i int, path string) {
    if i >= n + 1 {
        path = path[:len(path) - 1] // 去掉后面的那个空格
        ans = append(ans, path)
        return
    }

    for j := i; j < n + 1; j ++ {
        if f[j + 1] && S[s[i : j + 1]] {
            dfs(j + 1, path + s[i : j + 1] + " ")
        }
    }
}

func wordBreak(_s string, wordDict []string) []string {
    ans = []string{}
    n = len(_s)
    s = " " + _s
    S = make(map[string]bool)
    for _, x := range wordDict {
        S[x] = true
    }

    f = make([]bool, n + 2)
    f[n + 1] = true

    for i := n; i > 0; i -- {  // 从后往前预处理f[]数组
        for j := i; j < n + 1; j ++ {
            if f[j + 1] && S[s[i : j + 1]] {
                f[i] = true
                break
            }
        }
    }

    dfs(1, "")
    return ans
}

func wordBreak(s string, wordDict []string) []string {
	S := make(map[string]struct{})
	for _, word := range wordDict {
		S[word] = struct{}{}
	}

	n := len(s)
	s = " " + s // 在字符串前添加一个空格来简化索引处理
	f := make([]bool, n + 1)
	f[0] = true

	// 使用一个二维切片来存储所有可能的解
	ans := make([][]string, n + 1)
	ans[0] = append(ans[0], "")

	for i := 1; i <= n; i ++ {
		for j := i; j > 0; j -- {
			if f[j - 1] {
				x := s[j : i + 1]
				if _, ok := S[x]; ok {
					f[i] = true
					for _, str := range ans[j - 1] {
						space := " "
						if str == "" {
							space = ""
						}
						ans[i] = append(ans[i], str + space + x)
					}
				}
			}
		}
	}
    
	return ans[n]
}

LC141 环形链表

func hasCycle(head *ListNode) bool {
    if head == nil || head.Next == nil {
        return false
    }
    
    slow, fast := head, head
    for fast != nil && fast.Next != nil {
        slow = slow.Next
        fast = fast.Next.Next
        if slow == fast {
            return true
        }
    }

    return false
}

LC142环形链表II

func detectCycle(head *ListNode) *ListNode {
    if head == nil || head.Next == nil {
        return nil
    }

    slow, fast := head, head
    for fast != nil && fast.Next != nil {
        slow = slow.Next
        fast = fast.Next.Next
        if slow == fast {
            slow = head
            for slow != fast {
                slow = slow.Next
                fast = fast.Next
            }
            return slow
        }
    }

    return nil
}

LC143 重排链表

func getMid(head *ListNode) *ListNode {
    slow, fast := head, head
    for fast != nil && fast.Next != nil {
        slow = slow.Next
        fast = fast.Next.Next
    }
    return slow
}

func reverseList(head *ListNode) *ListNode {
    var pre *ListNode = nil
    cur := head
    for cur != nil {
        nxt := cur.Next
        cur.Next = pre
        pre = cur
        cur = nxt
    }
    return pre
}

func reorderList(head *ListNode)  {
    mid := getMid(head)
    l1, l2 := head, reverseList(mid)
    for l2.Next != nil {
        nxt1, nxt2 := l1.Next, l2.Next
        l1.Next = l2
        l2.Next = nxt1
        l1, l2 = nxt1, nxt2
    }
}

LC144 二叉树的前序遍历

var ans []int

func dfs(root *TreeNode) {
    if root == nil {
        return
    }
    ans = append(ans, root.Val)
    if root.Left != nil {
        dfs(root.Left)
    }
    if root.Right != nil {
        dfs(root.Right)
    }
}

func preorderTraversal(root *TreeNode) []int {
    if root == nil {
        return []int{}
    }
    ans = []int{}
    dfs(root)
    return ans
}

func preorderTraversal(root *TreeNode) []int {
    if root == nil {
        return nil
    }

    ans, stk := []int{}, []*TreeNode{}
    stk = append(stk, root)
    for len(stk) > 0 {
        t := stk[len(stk) - 1]
        stk = stk[:len(stk) - 1]
        ans = append(ans, t.Val)
        if t.Right != nil {
            stk = append(stk, t.Right)
        }
        if t.Left != nil {
            stk = append(stk, t.Left)
        }
    }
    
    return ans
}

func preorderTraversal(root *TreeNode) []int {
    if root == nil {
        return nil
    }

    ans := []int{}
    for root != nil {
        if root.Left == nil {
            ans = append(ans, root.Val)
            root = root.Right
        } else {
            p := root.Left
            for p.Right != nil && p.Right != root {
                p = p.Right
            }
            if p.Right == nil {
                p.Right = root
                ans = append(ans, root.Val)
                root = root.Left
            } else {
                p.Right = nil
                root = root.Right
            }
        }
    }

    return ans
}

LC145 二叉树的后序遍历

var ans []int

func dfs(root *TreeNode) {
    if root == nil {
        return
    }
    
    if root.Left != nil {
        dfs(root.Left)
    }
    if root.Right != nil {
        dfs(root.Right)
    }
    ans = append(ans, root.Val)
}

func postorderTraversal(root *TreeNode) []int {
    if root == nil {
        return nil
    }
    ans = []int{}
    dfs(root)
    return ans
}

func postorderTraversal(root *TreeNode) []int {
    if root == nil {
        return nil
    }
    ans, stk := []int{}, []*TreeNode{}
    stk = append(stk, root)
    for len(stk) > 0 {
        t := stk[len(stk) - 1]
        stk = stk[:len(stk) - 1]
        ans = append(ans, t.Val)
        if t.Left != nil {
            stk = append(stk, t.Left)
        }
        if t.Right != nil {
            stk = append(stk, t.Right)
        }
    }

    for i, j := 0, len(ans) - 1; i < j; i, j = i + 1, j - 1 {
        ans[i], ans[j] = ans[j], ans[i]
    }

    return ans
}

func postorderTraversal(root *TreeNode) []int {
    if root == nil {
        return nil
    }
    
    ans := []int{}
    for root != nil {
        if root.Right == nil {
            ans = append(ans, root.Val)
            root = root.Left
        } else {
            p := root.Right
            for p.Left != nil && p.Left != root {
                p = p.Left
            }
            if p.Left == nil {
                p.Left = root
                ans = append(ans, root.Val)
                root = root.Right
            } else {
                p.Left = nil
                root = root.Left
            }
        }
    }

    for i, j := 0, len(ans) - 1; i < j; i, j = i + 1, j - 1 {
        ans[i], ans[j] = ans[j], ans[i]
    }

    return ans
}

LC146 LRU缓存机制

class LRUCache {
public:
    struct Node {
        int key, val;
        Node *prior, *next;
        Node(int _key, int _val): key(_key), val(_val), prior(nullptr), next(nullptr) {}
    } *L, *R;
    unordered_map mp;
    int n;

    void del(Node *p) {
        p->prior->next = p->next;
        p->next->prior = p->prior;
    }

    void ins(Node *p) {
        p->prior = L;
        p->next = L->next;
        L->next->prior = p;
        L->next = p;
    }

    LRUCache(int capacity) {
        n = capacity;
        L = new Node(-1, -1), R = new Node(-1, -1);
        L->next = R, R->prior = L;
    }
    
    int get(int key) {
        if (!mp.count(key)) return -1;
        auto p = mp[key];
        del(p), ins(p);
        return p->val;
    }
    
    void put(int key, int value) {
        if (mp.count(key)) {
            auto p = mp[key];
            p->val = value;
            del(p), ins(p);
        } else {
            if (mp.size() == n) {
                auto p = R->prior;
                del(p);
                mp.erase(p->key);
                delete p;
            }
            auto p = new Node(key, value);
            mp[key] = p;
            ins(p);
        }
    }
};

LC147 对链表进行插入排序

func insertionSortList(head *ListNode) *ListNode {
    dummy := &ListNode{}
    p := head
    for p != nil {
        cur := dummy
        nxt := p.Next
        for cur.Next != nil && cur.Next.Val <= p.Val {
            cur = cur.Next
        }
        p.Next = cur.Next
        cur.Next = p
        p = nxt
    }
    return dummy.Next
}

LC148 排序链表

func sortList(head *ListNode) *ListNode {
    if head == nil {
        return nil
    }
    n := 0
    for p := head; p != nil; p = p.Next {
        n ++
    }
    dummy := &ListNode{Val: -1, Next: head}

    for i := 1; i < n; i <<= 1 {
        cur := dummy
        for j := 1; j + i <= n; j += 2 * i {
            p := cur.Next
            q := p
            for k := 0; k < i; k ++ {
                q = q.Next
            }

            x, y := 0, 0
            for p != nil && q != nil && x < i && y < i {
                if p.Val <= q.Val {
                    cur.Next = p
                    cur = cur.Next
                    p = p.Next
                    x ++
                } else {
                    cur.Next = q
                    cur = cur.Next
                    q = q.Next
                    y ++
                }
            }
            for p != nil && x < i {
                cur.Next = p
                cur = cur.Next
                p = p.Next
                x ++                
            }
            for q != nil && y < i {
                cur.Next = q
                cur = cur.Next
                q = q.Next
                y ++  
            }

            cur.Next = q
        }
    }

    return dummy.Next
}

LC149 直线上最多的点数

func maxPoints(points [][]int) int {
    ans := 0
    for _, p := range points {
        verPoints, samePoints := 0, 0
        mp := map[float64]int{}
        for _, q := range points {
            if p[0] == q[0] && p[1] == q[1] {
                samePoints ++
            } else if p[0] == q[0] {
                verPoints ++
            } else {
                k := float64(q[1] - p[1]) / float64(q[0] - p[0])
                mp[k] ++
            }
        }

        cnt := verPoints
        for _, v := range mp {
            cnt = max(cnt, v)
        }
        ans = max(ans, cnt + samePoints)
    }

    return ans
}

func maxPoints(points [][]int) int {
    ans := 0
    for _, p := range points {
        mp := map[string]int{}
        samePoints, t := 0, 0
        for _, q := range points {
            dy, dx := q[1] - p[1], q[0] - p[0]
            if dy == 0 && dx == 0 {
                samePoints ++
                continue
            }

            GCD := gcd(dy, dx)
            if GCD != 0 {
                dy /= GCD
                dx /= GCD
            }

            slope := fmt.Sprintf("%d/%d", dy, dx)
            mp[slope] ++
            t = max(t, mp[slope])
        }
        ans = max(ans, t + samePoints)
    }
    return ans
}

func gcd(a, b int) int {
    if b == 0 {
        return a
    }
    return gcd(b, a % b)
}

LC150 逆波兰表达式求值

func evalRPN(tokens []string) int {
    stk := []int{}
    for _, s := range tokens {
        if s == "+" || s == "-" || s == "*" || s == "/" {
			b, a := stk[len(stk) - 1], stk[len(stk) - 2]
			stk = stk[:len(stk) - 2]
            if s == "+" {
                a += b
            } else if s == "-" {
                a -= b
            } else if s == "*" {
                a *= b
            } else if s == "/" {
                a /= b
            }
            stk = append(stk, a)
        } else {
            if x, err := strconv.Atoi(s); err == nil {
                stk = append(stk, x)
            }
        }
    }
    return stk[len(stk) - 1]
}

LC151 反转字符串中的单词

func reverseWords(s string) string {
    ans := ""
    i, j := len(s) - 1, len(s) - 1
    for i >= 0 {
        for i >= 0 && s[i] == ' ' {
            i --
        }
        if i < 0 {
            break
        }
        j = i
        for i >= 0 && s[i] != ' ' {
            i --
        }
        if len(ans) > 0 {
            ans += " "
        }
        ans += s[i + 1 : j + 1]
    }
    return ans
}

LC152 乘积最大子数组

func maxProduct(nums []int) int {
    n := len(nums)
    f, g := make([]int, n), make([]int, n)
    f[0], g[0] = nums[0], nums[0]
    var ans int = f[0]
    for i := 1; i < n; i ++ {
        if nums[i] >= 0 {
            f[i] = max(nums[i], f[i - 1] * nums[i])
            g[i] = min(nums[i], g[i - 1] * nums[i])
        } else {
            f[i] = max(nums[i], g[i - 1] * nums[i])
            g[i] = min(nums[i], f[i - 1] * nums[i])
        }
        ans = max(ans, f[i])
    }

    return ans
}

func maxProduct(nums []int) int {
    ans, f, g := nums[0], nums[0], nums[0]
    for i := 1; i < len(nums); i ++ {
        a:= nums[i]
        fa, ga := f * a, g * a
        f = max(a, max(fa, ga))
        g = min(a, min(fa, ga))
        ans = max(ans, f)
    }
    return ans
}

LC153 寻找旋转排序数组中的最小值

func findMin(nums []int) int {
    l, r := 0, len(nums) - 1
    for l < r {
        mid := (l + r) >> 1
        if nums[mid] < nums[r] {
            r = mid
        } else {
            l = mid + 1
        }
    }
    return nums[r]
}

LC154 寻找旋转排序数组中的最小值II

func findMin(nums []int) int {
    n := len(nums) - 1
    for n >= 0 && nums[n] == nums[0] {
        n --
    }
    if n < 0 {
        return nums[0]
    }

    l, r := 0, n
    for l < r {
        mid := (l + r) >> 1
        if nums[mid] <= nums[r] {
            r = mid
        } else {
            l = mid + 1
        }
    }

    return nums[r]
}

LC155 最小栈

class MinStack {
public:
    stack> stk;
    MinStack() {}
    
    void push(int x) {
        if (stk.empty())    stk.push({x, x});
        else    stk.push({x, min(x, stk.top().second)});
    }
    
    void pop() {
        stk.pop();
    }
    
    int top() {
        return stk.top().first;
    }
    
    int getMin() {
        return stk.top().second;
        
    }
};

class MinStack {
public:
    stack stk, min_stk;
    MinStack() {}
    
    void push(int x) {
        stk.push(x);
        if (min_stk.empty() || x <= min_stk.top())  {
            min_stk.push(x);
        }
    }
    
    void pop() {
        if (stk.top() == min_stk.top()) min_stk.pop();
        stk.pop();
    }
    
    int top() {
        return stk.top();
    }
    
    int getMin() {
        return min_stk.top();
    }
};

// 时空复杂度都为O(1)
class MinStack {
public:
    using LL = long long ;
    vector stk; // 注意栈内是LL 而不是int
    int minVal = INT_MAX;
    MinStack() {}
    
    void push(int val) {
        if (stk.empty())    minVal = val;
        // 注意val - minVal可能会导致溢出  这里转为LL
        stk.push_back((LL)val - minVal);
        if (val < minVal)   minVal = val;
    }
    
    void pop() {
        LL x = stk.back(); stk.pop_back();
        if (x < 0)  minVal -= x;
    }
    
    int top() {  // 这里返回值也可以写LL
        LL x = stk.back();
        return x >= 0 ? minVal + x : minVal;
    }
    
    int getMin() {  // 这里返回值也可以写LL
        return minVal;
    }
};

LC156 上下翻转二叉树

func dfs(x, y *TreeNode) *TreeNode {
    var rt *TreeNode
    if y.Left != nil {
        rt = dfs(y, y.Left)
    } else {
        rt = y
    }
    if x != nil {
        z := x.Right
        y.Left, y.Right = z, x
        x.Left, x.Right = nil, nil
    }
    return rt
}

func upsideDownBinaryTree(root *TreeNode) *TreeNode {
    if root == nil {
        return nil
    }
    return dfs(nil, root)
}

func upsideDownBinaryTree(root *TreeNode) *TreeNode {
    if root == nil {
        return nil
    }
    var p *TreeNode = nil
    var p_rc *TreeNode = nil
    for root != nil {
        l, r := root.Left, root.Right
        root.Left, root.Right = p_rc, p
        p, root, p_rc = root, l, r
    }
    return p
}

LC159 至多包含两个不同字符的最长子串

func lengthOfLongestSubstringTwoDistinct(s string) int {
	ans, cnt := 0, 0
	mp := map[byte]int{}
	for l, r := 0, 0; r < len(s); r ++ {
		if mp[s[r]] == 0 {
			cnt ++
		}
		mp[s[r]] ++
		for cnt > 2 {
			mp[s[l]] --
			if mp[s[l]] == 0 {
				cnt --
			}
			l ++
		}
		ans = max(ans, r - l + 1)
	}
	return ans
}

LC160 相交链表

func getIntersectionNode(headA, headB *ListNode) *ListNode {
    p, q := headA, headB
    for p != q {
        if p != nil {
            p = p.Next
        } else {
            p = headB
        }

        if q != nil {
            q = q.Next
        } else {
            q = headA
        }
    }
    return p
}

LC161 相隔为1的编辑距离

func isOneEditDistance(s string, t string) bool {
    m, n := len(s), len(t)
    if m > n {
        return isOneEditDistance(t, s)
    }
    if n - m > 1 {
        return false
    }

    for i := 0; i < m; i ++ {
        if s[i] != t[i] {
            if m == n {
                return s[i + 1:] == t[i + 1:]
            } else {
                return s[i:] == t[i + 1:]
            }
        }
    }

    return m + 1 == n
}

LC162 寻找峰值

// 二分
func findPeakElement(nums []int) int {
    l, r := 0, len(nums) - 1
    for l < r {
        mid := (l + r) >> 1
        if nums[mid] > nums[mid + 1] {
            r = mid
        } else {
            l = mid + 1
        }
    }
    return l
}

// 三分
func findPeakElement(nums []int) int {
    l, r := 0, len(nums) - 1
    for l < r {
        m1 := (l + r) >> 1
        m2 := m1 + 1
        // m1 := l + (r - l) / 3
        // m2 := r - (r - l) / 3
        if nums[m1] < nums[m2] {
            l = m1 + 1
        } else {
            r = m2 - 1
        }
    }
    return l
}

LC163 缺失的区间

func findMissingRanges(nums []int, lower int, upper int) [][]int {
    nums = append([]int{lower - 1}, nums...)
    nums = append(nums, upper + 1)
    ans := [][]int{}
    for i := 1; i < len(nums); i ++ {
        if nums[i] - nums[i - 1] > 1 {
            ans = append(ans, []int{nums[i - 1] + 1, nums[i] - 1})
        }
    }
    return ans
}

LC164 最大间距

func maximumGap(nums []int) int {
    n := len(nums)
    if n < 2 {
        return 0
    }
    radix, maxVal := 1, 0
    for _, x := range nums {
        maxVal = max(maxVal, x)
    }

    tmp := make([]int, n)
    for radix <= maxVal {
        cnt := make([]int, 10)
        for _, x := range nums {
            digit := (x / radix) % 10
            cnt[digit] ++
        }

        for i := 1; i < 10; i ++ {
            cnt[i] += cnt[i - 1]
        }

        for i := n - 1; i >= 0; i -- {
            digit := (nums[i] / radix) % 10
            cnt[digit] --
            tmp[cnt[digit]] = nums[i]
        }

        copy(nums, tmp)

        radix *= 10
    }

    ans := 0
    for i := 1; i < n; i ++ {
        ans = max(ans, nums[i] - nums[i - 1])
    }

    return ans
}

LC165 比较版本号

func compareVersion(v1, v2 string) int {
	n, m := len(v1), len(v2)
	for i, j := 0, 0; i < n || j < m; i, j = i + 1, j + 1 {
		x, y := 0, 0
		for i < n && v1[i] != '.' {
			x = x * 10 + int(v1[i]-'0')
			i ++
		}
		for j < m && v2[j] != '.' {
			y = y * 10 + int(v2[j]-'0')
			j ++
		}
		if x > y {
			return 1
		}
		if x < y {
			return -1
		}
	}
	return 0
}

LC166 分数到小数

func fractionToDecimal(numerator int, denominator int) string {
    x, y := int64(numerator), int64(denominator)
    if x % y == 0 {
        return fmt.Sprintf("%d", x / y)
    }
    
    ans := ""
    if (x < 0) != (y < 0) {
        ans += "-"
    }

    x = abs(x)
    y = abs(y)
    ans += fmt.Sprintf("%d.", x / y)
    x %= y;

    mp := map[int64]int{}

    for x > 0 {
        mp[x] = len(ans)
        x *= 10
        ans += fmt.Sprintf("%d", x / y)
        x %= y

        if i, ok := mp[x]; ok {
            ans = ans[:i] + "(" + ans[i:] + ")"
            break
        }
    }

    return ans
}

func abs(x int64) int64 {
    if x < 0 {
        return -x
    }
    return x
}

LC167 两数之和II

func twoSum(nums []int, target int) []int {
    l, r := 0, len(nums) - 1
    for l < r {
        s := nums[l] + nums[r]
        if s == target {
            return []int{l + 1, r + 1}
        } else if s < target {
            l ++
        } else {
            r -- 
        }
    }

    return []int{-1, -1}
}

LC168 Excel列表名称

func convertToTitle(x int) string {
    ans := []byte{}
    for x > 0 {
        x --
        ans = append(ans, 'A' + byte(x % 26))
        x /= 26
    }

    for i, j := 0, len(ans) - 1; i < j; i, j = i + 1, j - 1 {
        ans[i], ans[j] = ans[j], ans[i]
    }

    return string(ans)
}

LC169 多数元素

func majorityElement(nums []int) int {
    p1, c1, n := 0, 0, len(nums)
    for _, x := range nums {
        if c1 > 0 && x == p1 {
            c1 ++
        } else if c1 == 0 {
            p1 = x
            c1 = 1
        } else {
            c1 --
        }
    }

    c1 = 0
    for _, x := range nums {
        if x == p1 {
            c1 ++
        }
    }

    if c1 > n / 2 {
        return p1
    }
    return 0
}

LC170 两数之和II-数据机构设计

type TwoSum struct {
    mp map[int]int
}

func Constructor() TwoSum {
    return TwoSum{mp: make(map[int]int)}
}

func (this *TwoSum) Add(x int)  {
    this.mp[x] ++
}

func (this *TwoSum) Find(value int) bool {
    for x, cnt := range this.mp {
        y := value - x
        if y != x {
            if _, ok := this.mp[y]; ok {
                return true
            }
        } else if cnt >= 2 {
            return true
        }
    }
    return false
}

LC171 Excel表序列号

func titleToNumber(s string) int {
    ans := 0
    for _, c := range s {
        ans = ans * 26 + (int(c - 'A') + 1)
    }
    return ans
}

LC172 阶乘后的零

// 迭代
func trailingZeroes(n int) int {
    ans, p := 0, 5
    for n > 0 {
        ans += n / p
        n /= p
    }
    return ans
}

// 递归
class Solution {
public:
    int p = 5;
    int trailingZeroes(int n) {
        if (n < p)  return 0;
        return n / p + trailingZeroes(n / p);
    }
};

LC173 二叉搜索树迭代器

type BSTIterator struct {
    root *TreeNode
    stk []*TreeNode
}


func Constructor(rt *TreeNode) BSTIterator {
    return BSTIterator{root: rt}
}


func (this *BSTIterator) Next() int {
    for this.root != nil {
        this.stk = append(this.stk, this.root)
        this.root = this.root.Left
    }
    this.root = this.stk[len(this.stk) - 1]
    this.stk = this.stk[ : len(this.stk) - 1]
    x := this.root.Val
    this.root = this.root.Right
    return x
}


func (this *BSTIterator) HasNext() bool {
    return len(this.stk) > 0 || this.root != nil
}

LC174 地下城游戏

func calculateMinimumHP(w [][]int) int {
    n, m := len(w), len(w[0])
    f := make([][]int, n + 1)
    for i := 0; i < n + 1; i ++ {
        f[i] = make([]int, m + 1)
        for j := 0; j < m + 1; j ++ {
            f[i][j] = math.MaxInt32
        }
    }

    f[n][m - 1], f[n - 1][m] = 1, 1
    for i := n - 1; i >= 0; i -- {
        for j := m - 1; j >= 0; j -- {
            f[i][j] = max(1, min(f[i + 1][j], f[i][j + 1]) - w[i][j])
        }
    }

    return f[0][0]
}

func calculateMinimumHP(w [][]int) int {
    n, m := len(w), len(w[0])
    f := make([][]int, n + 1)
    for i := 0; i < n + 1; i ++ {
        f[i] = make([]int, m + 1)
        for j := 0; j < m + 1; j ++ {
            f[i][j] = math.MaxInt32
        }
    }

    for i := n - 1; i >= 0; i -- {
        for j := m - 1; j >= 0; j -- {
            if i == n - 1 && j == m - 1 {
                f[i][j] = max(1, 1 - w[i][j])
            } else {
                if i + 1 < n {
                    f[i][j] = min(f[i][j], f[i + 1][j] - w[i][j]);
                }
                if j + 1 < m {
                    f[i][j] = min(f[i][j], f[i][j + 1] - w[i][j]);
                }
                f[i][j] = max(1, f[i][j])
            }
        }
    }

    return f[0][0]
}

LC179 最大数

func largestNumber(nums []int) string {
    sort.Slice(nums, func(i, j int) bool {
        a, b := strconv.Itoa(nums[i]), strconv.Itoa(nums[j])
        return a + b > b + a
    })
    if nums[0] == 0 {
        return "0"
    }
    ans := ""
    for _, x := range nums {
        ans += strconv.Itoa(x)
    }
    return ans
}

LC187 重复的DNA序列

func findRepeatedDnaSequences(s string) []string {
    ans := []string{}
    mp := map[string]int{}
    for i := 0; i + 9 < len(s); i ++ {
        t := s[i : i + 10]
        mp[t] ++
        if mp[t] == 2 {
            ans = append(ans, t)
        }
    }
    return ans
}

const base = 13331
var (
    h, p []uint64
)

func get(l, r int) uint64 {
    return h[r] - h[l - 1] * p[r - l + 1]
}

func findRepeatedDnaSequences(s string) []string {
	n := len(s)
	s = " " + s
	h, p = make([]uint64, n + 1), make([]uint64, n + 1)
	p[0] = 1

	for i := 1; i <= n; i++ {
		h[i] = h[i - 1] * base + uint64(s[i])
		p[i] = p[i - 1] * base
	}

	var ans []string
	mp := map[uint64]int{}

	for i := 1; i + 9 < n + 1; i ++ {
		x := get(i, i + 9)
		mp[x] ++
		if mp[x] == 2 {
			ans = append(ans, s[i : i + 10])
		}
	}

	return ans
}

LC188 买卖股票的最佳时机 IV

func maxProfit(k int, prices []int) int {
	n := len(prices)
	prices = append([]int{-1}, prices...)
	f := make([][][]int, n + 1)

	for i := range f {
		f[i] = make([][]int, k + 1)
		for j := range f[i] {
			f[i][j] = make([]int, 2)
		}
	}

	for j := 0; j <= k; j ++ {
		f[0][j][1] = math.MinInt
	}

	for i := 1; i <= n; i ++ {
		for j := 1; j <= k; j ++ {
			f[i][j][0] = max(f[i - 1][j][0], f[i - 1][j][1] + prices[i])
			f[i][j][1] = max(f[i - 1][j][1], f[i - 1][j-1][0] - prices[i])
		}
	}

	return f[n][k][0]
}

func maxProfit(k int, prices []int) int {
	n := len(prices)
	prices = append([]int{-1}, prices...)
	f := make([][]int, k + 1)

	for i := range f {
		f[i] = make([]int, 2)
	}

	for j := 0; j <= k; j ++ {
		f[j][1] = math.MinInt
	}

	for i := 1; i <= n; i ++ {
		for j := 1; j <= k; j ++ {
			f[j][0] = max(f[j][0], f[j][1] + prices[i])
			f[j][1] = max(f[j][1], f[j - 1][0] - prices[i])
		}
	}

	return f[k][0]
}

LC189 轮转数组

// 时间复杂度O(n) 空间复杂度O(n)
func rotate(nums []int, k int)  {
    n := len(nums)
    tmp := make([]int, n)
    for i := 0; i < n; i ++ {
        tmp[(i + k) % n] = nums[i]
    }
    copy(nums, tmp)
}

// 时间复杂度O(n) 空间复杂度O(1)
func rotate(nums []int, k int)  {
    n := len(nums)
    k %= n
    reverse(nums, 0, n - 1)
    reverse(nums, 0, k - 1)
    reverse(nums, k, n - 1)
}

func reverse(nums []int, l, r int) {
    for l < r {
        nums[l], nums[r] = nums[r], nums[l]
        l ++
        r --
    }
}

// //时间复杂度O(n) 空间复杂度O(1)
func rotate(nums []int, k int)  {
    n := len(nums)
    k %= n
    cnt := gcd(k, n)
    for start := 0; start < cnt; start ++ {
        cur, prev := start, nums[start]
        for {
            nxt := (cur + k) % n
            nums[nxt], prev = prev, nums[nxt]
            cur = nxt
            if cur == start {
                break
            }
        }
    }
}

func gcd(a, b int) int {
    if b == 0 {
        return a
    }
    return gcd(b, a % b)
}

LC190 颠倒二进制位

func reverseBits(n uint32) uint32 {
    var ans uint32
    for i := 0; i < 32; i ++ {
        ans = (ans << 1) + (n >> i & 1)
    }
    return ans
}

LC191 位1的个数

func hammingWeight(n uint32) int {
    ans := 0
    for i := 0; i < 32; i ++ {
        ans += int(n >> i) & 1
    }
    return ans
}

func hammingWeight(n uint32) int {
    ans := 0
    for n > 0 {
        n -= n & -n
        ans ++
    }
    return ans
}

LC198 打家劫舍

func rob(nums []int) int {
    n := len(nums)
    if n == 0 {
        return 0
    }
    if n == 1 {
        return nums[0]
    }

    f := make([]int, n)
    f[0], f[1] = nums[0], max(nums[0], nums[1])
    for i := 2; i < n; i ++ {
        f[i] = max(f[i - 1], f[i - 2] + nums[i])
    }

    return f[n - 1]
}

func rob(nums []int) int {
    n := len(nums)
    if n == 0 {
        return 0
    }
    if n == 1 {
        return nums[0]
    }

    a, b := nums[0], max(nums[0], nums[1])
    for i := 2; i < n; i ++ {
        tmp := b
        b = max(b, a + nums[i])
        a = tmp
    }

    return b
}

LC199 二叉树的右视图

var ans []int

func dfs(root *TreeNode, dep int) {
    if root == nil {
        return
    }

    if dep == len(ans) {
        ans = append(ans, root.Val)
    }

    if root.Right != nil {
        dfs(root.Right, dep + 1)
    }
    if root.Left != nil {
        dfs(root.Left, dep + 1)
    }
}

func rightSideView(root *TreeNode) []int {
    if root == nil {
        return []int{}
    }
    ans = []int{}
    dfs(root, 0)
    return ans
}

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func rightSideView(root *TreeNode) []int {
	var ans []int
	if root == nil {
		return ans
	}

	q := []*TreeNode{root}
	for len(q) > 0 {
		s := len(q)
		for i := 0; i < s; i ++ {
			t := q[0]
			q = q[1:]

			if i == s - 1 {   // 当前层的最后一个节点
				ans = append(ans, t.Val)
			}

			if t.Left != nil {
				q = append(q, t.Left)
			}
			if t.Right != nil {
				q = append(q, t.Right)
			}
		}
	}

	return ans
}

LC200 岛屿数量

type PII struct {
	x, y int
}

var (
    g [][]byte
    n, m int
	dx = []int{-1, 0, 1, 0}
	dy = []int{0, 1, 0, -1}
)

func bfs(sx, sy int) {
	q := []PII{{sx, sy}}
	g[sx][sy] = '#' // 标记点(sx,sy)已经被访问过了

	for len(q) > 0 {
		t := q[0]
		q = q[1:]

		for i := 0; i < 4; i ++ {
			a, b := t.x + dx[i], t.y + dy[i]
			if a < 0 || a >= n || b < 0 || b >= m || g[a][b] == '#' || g[a][b] == '0' {
				continue
			}
			q = append(q, PII{a, b})
			g[a][b] = '#' // 标记点(a,b)已经被访问过了
		}
	}
}

func numIslands(grid [][]byte) int {
    g = grid

	n, m = len(g), len(g[0])
    if n == 0 || m == 0 {
        return 0
    }
    
	ans := 0
	for i := 0; i < n; i ++ {
		for j := 0; j < m; j ++ {
			// 如果点(i,j)没有被访问过并且它是陆地
			if g[i][j] != '#' && g[i][j] == '1' {
				bfs(i, j)
				ans ++
			}
		}
	}

	return ans
}

var (
    g [][]byte
    n, m int
	dx = []int{-1, 0, 1, 0}
	dy = []int{0, 1, 0, -1}
)

func dfs(x, y int) {
	g[x][y] = '#'
	for i := 0; i < 4; i ++ {
		a, b := x + dx[i], y + dy[i]
		if a < 0 || a >= n || b < 0 || b >= m || g[a][b] != '1' {
			continue
		}
		dfs(a, b)
	}
}


func numIslands(grid [][]byte) int {
    g = grid

    n, m = len(g), len(g[0])
	if n == 0 || m == 0 {
		return 0
	}

    ans := 0
	for i := 0; i < n; i ++ {
		for j := 0; j < m; j ++ {
			// 如果点(i,j)没有被访问过并且它是陆地
			if g[i][j] != '#' && g[i][j] == '1' {
				dfs(i, j)
				ans ++
			}
		}
	}

	return ans
}

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