[LeetCode Hot 100] LeetCode543. 二叉树的直径

题目描述

思路

所谓二叉树的直径，就是左右子树的最大深度之和。

方法一：

/**
 * 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 {
    private int res = 0;
    public int diameterOfBinaryTree(TreeNode root) {
        postOrder(root);
        return res;
    }
    private int postOrder(TreeNode node) {
        if (node == null) return 0;
        int leftMaxDepth = postOrder(node.left);
        int rightMaxDepth = postOrder(node.right);
        res = Math.max(res, leftMaxDepth + rightMaxDepth);
        return Math.max(leftMaxDepth, rightMaxDepth) + 1;
    }
}