Leetcode OJ平台上的MaximumDepthofBinaryTree题目用Java递归实现

原题目如下：

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.

使用java递归实现如下：

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