leetCode练习（104）

题目：Maximum Depth of Binary Tree

难度：easy

问题描述：

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.

解题思路：

求二叉树的层数，使用dfs深度搜索，层数=1+max（左子树层数，右子树层数）。

代码如下：

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