[LeetCode] MaximumDepth of Binary Tree

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.

 /**
  * Definition for binary tree
  * 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 == NULL) return ;

         int left_depth = maxDepth(root->left);
         int right_depth = maxDepth(root->right);

         return left_depth > right_depth ? left_depth +  : right_depth + ;
     }
 };