1 class Solution {
 2 public:
 3     //非递归方法(利用队列实现)
 4     int maxDepth(TreeNode* root) 
 5     {
 6         if (NULL == root)
 7         {
 8             return 0;
 9         }
10         std::queue<TreeNode *> tQue;
11         tQue.push(root);
12         int ndepth = 0;
13         while (!tQue.empty())
14         {
15             ndepth++;
16             int nSize = tQue.size();            
17             for (int i=0; i<nSize; i++)
18             {
19                 TreeNode *pCur = tQue.front();
20                 tQue.pop();
21                 if (NULL != pCur->left)
22                 {
23                     tQue.push(pCur->left);
24                 }
25                 if (NULL != pCur->right)
26                 {
27                     tQue.push(pCur->right);
28                 }
29             }
30         }
31         return ndepth;
32     }
33     //递归实现（运行时间超时）
34     int maxDepth_1(TreeNode* root) 
35     {
36         if (NULL == root)
37         {
38             return 0;
39         }
40         return 1+(maxDepth(root->left)>maxDepth(root->right) ? maxDepth(root->left):maxDepth(root->right));
41     }
42 };