【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.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3

   / \

  9  20

    /  \

   15   7

return its depth = 3.

【思路】

递归，1+Math.max(maxDepth(root.left),maxDepth(root.right));

【解答】

class Solution {

public int maxDepth(TreeNode root) {

if(root==null)

return 0;

  return 1+Math.max(maxDepth(root.left),maxDepth(root.right));

}

}

【其他定义】

* Definition for a binary tree node.

* public class TreeNode {

*     int val;

*     TreeNode left;

*     TreeNode right;

*     TreeNode(int x) { val = x; }

* }

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