104. Maximum Depth of Binary Tree

A classic DFS solution on tree again.

1:  /**  
2:   * Definition for a binary tree node.  
3:   * struct TreeNode {  
4:   *   int val;  
5:   *   TreeNode *left;  
6:   *   TreeNode *right;  
7:   *   TreeNode(int x) : val(x), left(NULL), right(NULL) {}  
8:   * };  
9:   */  
10:  class Solution {  
11:  public:  
12:    int maxDepth(TreeNode* root) {  
13:      if (root == NULL) return 0;  
14:      return 1 + max(maxDepth(root->left), maxDepth(root->right));  
15:    }  
16:  };