543. 二叉树的直径

https://leetcode-cn.com/problems/diameter-of-binary-tree/

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    int ans;
    public int diameterOfBinaryTree(TreeNode root) {
        ans = 1;
        depth(root);
        return ans-1;
    }
    public int depth(TreeNode root){
        if(root==null) return 0;
        int left = depth(root.left);
        int right = depth(root.right);
        ans = Math.max(left+right+1,ans);
        return Math.max(left,right)+1;
    }
}