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

/**
* 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;
}
};