LC.P124[二叉树中的最大路径和]

方法一：DFS

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/**
 * 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 {
    
    int ans = Integer.MIN_VALUE;

    public int maxPathSum(TreeNode root) {
        dfs(root);
        return ans;
    }

    private int dfs(TreeNode root) {
        if (root == null) return 0;
        int left = dfs(root.left);
        int right = dfs(root.right);
        int sum = root.val;
        if (left >= 0) sum += left;
        if (right >= 0) sum += right;
        ans = Math.max(ans, sum);
        return Math.max(root.val, Math.max(left, right) + root.val);
    }
}
  • 时间复杂度：$O(n)$
  • 空间复杂度：$O(n)$