Day73x.算法训练

337. 打家劫舍 III

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int rob(TreeNode root) {
        int[] ints = rob2(root);

        return Integer.max(ints[0], ints[1]);
    }

    public int[] rob2(TreeNode cur) {
        if (cur == null) {
            return new int[] {0, 0};
        }
        int[] leftDp = rob2(cur.left);

        int[] rightDp = rob2(cur.right);

        int i1 = cur.val + leftDp[0] + rightDp[0];
        int i2 = Integer.max(leftDp[0], leftDp[1]) + Integer.max(rightDp[0], rightDp[1]);
        return new int[] {i2, i1};
    }
}

11. 盛最多水的容器

class Solution {
    public int maxArea(int[] height) {
        int i = 0;
        int j = height.length - 1;

        int max = 0;
        while (i < j) {
            if (height[i] < height[j]) {
                int area = (j - i) * height[i];
                max = Integer.max(max, area);
                i++;
            } else {
                int area = (j - i) * height[j];
                max = Integer.max(max, area);
                j--;
            }
        }
        return max;
    }
}

216. 组合总和 III

class Solution {

    List path = new ArrayList<>();

    List> result = new ArrayList<>();

    public List> combinationSum3(int k, int n) {
        int sum = 0;
        combinationSum3(k, n, sum, 1);
        return result;
    }

    private void combinationSum3(int k, int n, int sum, int startX) {
        if (path.size() == k) {
            if (sum == n) {
                result.add(new ArrayList<>(path));
            }
            return;
        }
        if (sum > n) {
            return;
        }
        for (int i = startX; i <= 9 - (k - path.size()) + 1; i++) {
            path.add(i);
            sum += i;

            combinationSum3(k, n, sum, i + 1);

            path.remove(path.size() - 1);
            sum -= i;
        }
    }
}

239. 滑动窗口最大值

class Solution {

    LinkedList queue = new LinkedList<>();

    public int[] maxSlidingWindow(int[] nums, int k) {
        List res = new ArrayList<>(nums.length);
        for (int i = 0; i < nums.length; i++) {
            if (i >= k) {
                pop(nums[i - k]);
            }
            offer(nums[i]);
            if (i + 1 >= k) {
                res.add(peek());
            }
        }
        return res.stream().mapToInt(Integer::intValue).toArray();
    }

    public void offer(int val) {
        while (!queue.isEmpty() && val > queue.peekLast()) {
            queue.removeLast();
        }
        queue.addLast(val);
    }

    public int peek() {
        return queue.peekFirst();
    }

    public void pop(int val) {
        if (!queue.isEmpty() && val == queue.peekFirst()) {
            queue.pollFirst();
        }
    }
}