二叉树的最大深度

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.

/**

* 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;

// 递归计算左子树深度

l = maxDepth(root.left);

// 递归计算右子树深度

r = maxDepth(root.right);

// 判断左右子树哪一个大则加一

return l>r?l+1:r+1;

}

}