leetcode-104. Maximum Depth of Binary Tree

题目：

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

找最大深度，这题我用了一个域变量去做，这样就比较简单了。当然也可以不用但是比较麻烦。

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    private int dep = 0;    public int maxDepth(TreeNode root) {        helper(root,1);        return dep;    }    private void helper(TreeNode root, int i){        if(root ==null) return ;        dep = Math.max(dep,i);        helper(root.left,i+1);        helper(root.right,i+1);    }}