从零开始的刷LeetCode生活 第51期 557-575

class Solution {
public:
    string reverseWords(string s) {
        int front = 0, back = 0;
        for(int i = 0; i < s.size(); i ++)
        {
            if(s[i] != ' ') back ++;
            else
            {
                reverse(s.begin() + front, s.begin() + back);
                front = back + 1;
                back = front;
            }
        }
        reverse(s.begin() + front, s.begin() + back);
        return s;
    }
};

class Solution {
public:
    string reverseWords(string s) {
        int n = s.size();
        int start = 0, back = 0;
        for(int i = 0; i < n + 1; i ++)
        {
            if(s[i] == ' ' || s[i] == '\0')
            {
                //cout << start << ' ' << back << endl;
                for(back = i - 1; start < back; start ++, back --)
                    swap(s[start], s[back]);
                start = i + 1;
            }            
        }        
        return s;
    }
};

/*
// Definition for a Node.
class Node {
public:
    int val;
    vector children;

    Node() {}

    Node(int _val) {
        val = _val;
    }

    Node(int _val, vector _children) {
        val = _val;
        children = _children;
    }
};
*/
class Solution {
public:
    int maxDepth(Node* root) {
        if(!root) return 0;
        int d = 1;
        for(auto s : root->children)
            d = max(d, maxDepth(s) + 1);
        return d;
    }
};

class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        unordered_map<int, int>hash;
        hash[0] = 1;
        int res = 0, s = 0;
        for(auto x : nums)
        {
            s += x;
            res += hash[s - k];
            hash[s] ++;
        }
        return res;
    }
};

class Solution {
public:
    int arrayPairSum(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        int res = 0;
        for(int i = 0; i < nums.size(); i += 2)
            res += min(nums[i], nums[i + 1]);
        return res;
    }
};

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int findTilt(TreeNode* root) {
        int res = 0;
        dfs(root, res);
        return res;
    }

    int dfs(TreeNode* root, int &res)
    {
        if(!root) return 0;
        int left = dfs(root->left, res);
        int right = dfs(root->right, res);
        res += abs(left - right);
        return root->val + left + right; 
    }
};

class Solution {
public:
    string nearestPalindromic(string n) {
        long long N = stol(n), len = n.size();
        set<long long>s;
        s.insert(pow(10, len) + 1); // 进位 99 -> 100
        s.insert(pow(10, len - 1) - 1); //退位 100 -> 99
        long long prefix = stol(n.substr(0, (len + 1) / 2));
        for(int i = -1; i <= 1; i++)
        {
            string pre = to_string(prefix + i);
            s.insert(stol(pre + string(pre.rbegin() + (len & 1), pre.rend())));
        }
        s.erase(N); //去掉相同的
        long long res = -1, min = LLONG_MAX;
        for(auto val : s)
        {
            long long diff = abs(N - val);
            if(diff < min)
            {
                min = diff;
                res = val;
            }
        }
        return to_string(res);
    }
};

class Solution {
public:
    int arrayNesting(vector<int>& nums) {
        int res = 0;
        for(int i = 0; i < nums.size(); i ++)
        {
            int start = nums[i], count = 0;
            if(nums[i] == -1) continue;
            nums[i] = -1;
            do{
                start = nums[start];
                count ++;
            }while(start != nums[i]);
            res = max(res, count);
        }
        return res;
    }
};

class Solution {
public:
    int arrayNesting(vector<int>& nums) {
        int res = 0;
        for(int i = 0; i < nums.size(); i ++)
        {
            if(nums[i] != -1)
            {
                int start = nums[i], count = 0;
                while(nums[start] != -1)
                {
                    int tmp = start;
                    start = nums[start];
                    count ++;
                    nums[tmp] = -1;
                }
                res = max(res, count);
            }
        }
        return res;
    }
};

class Solution {
public:
    vector<vector<int>> matrixReshape(vector<vector<int>>& nums, int r, int c) {
        int n = nums.size(), m = nums[0].size();
        if(r * c != n * m) return nums;
        vector<vector<int>>res(r, vector<int>(c));
        for(int i = 0; i < n * m; i ++)
            res[i / c][i % c] = nums[i / m][i % m];
        return res;
    }
};

class Solution {
public:
    bool checkInclusion(string s1, string s2) {
        if(s1.size() > s2.size()) return false;
        int windowSize = s1.size();
        vector<int>hash1(26, 0);
        vector<int>hash2(26, 0);
        for(int i = 0; i < windowSize; i ++)
        {
            hash1[s1[i] - 'a'] ++;
            hash2[s2[i] - 'a'] ++;
        }
        for(int i = windowSize; i < s2.size(); i ++)
        {
            if(hash1 == hash2) return true;
            hash2[s2[i - windowSize] - 'a'] --;
            hash2[s2[i] - 'a'] ++;
        }
        return hash1 == hash2;
    }
};

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isSubtree(TreeNode* s, TreeNode* t) {
        if(s == NULL && t == NULL) return true;
        if(s == NULL && t != NULL) return false;
        return isSametree(s, t) || isSubtree(s->left, t) || isSubtree(s->right, t);
    }

    bool isSametree(TreeNode*s, TreeNode* t)
    {
        if(s == NULL && t == NULL) return true;
        return s && t && (s->val == t->val) 
                && isSametree(s->left, t->left)
                && isSametree(s->right, t->right);
    }
};

class Solution {
public:
    int distributeCandies(vector<int>& candies) {
        set<int> s(candies.begin(), candies.end());
        return min(s.size(), candies.size() >> 1);
    }
};

class Solution {
public:
    int distributeCandies(vector<int>& candies) {
        unordered_map<int, int>hash;
        for(int x : candies)
            hash[x] ++;
        //cout << hash.size();
        return min(hash.size(), candies.size() >> 1);
    }
};