LeetCode Maximum Depth of Binary Tree (求树的深度)

题意：给一棵二叉树，求其深度。

思路：递归比较简洁，先求左子树深度，再求右子树深度，比较其结果，返回：max_one+1。

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode* root) {
        if(!root)   return 0;
        int a=maxDepth(root->left);
        int b=maxDepth(root->right);
        return a>b?a+1:b+1;
    }
};