【树】95. 不同的二叉搜索树 II

 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     vector<TreeNode *> generate(int beg, int end)
13     {
14         vector<TreeNode* > ret;
15 
16         if (beg > end)
17         {
18             ret.push_back(NULL);
19             return ret;
20         }
21 
22         for(int i = beg; i <= end; i++)
23         {
24             vector<TreeNode* > leftTree = generate(beg, i - 1);
25             vector<TreeNode* > rightTree = generate(i + 1, end);
26 
27             for(int j = 0; j < leftTree.size(); j++)
28             {
29                 for(int k = 0; k < rightTree.size(); k++)
30                 {
31                     TreeNode *node = new TreeNode(i);
32                     ret.push_back(node);
33                     node->left = leftTree[j];
34                     node->right = rightTree[k];
35                 }
36             }                
37         }
38         return ret;
39     }
40     
41     vector<TreeNode *> generateTrees(int n)
42     {
43         vector<TreeNode*> ret;
44         if (0 == n)
45         {
46             return ret;
47         }
48         
49         ret = generate(1, n);
50         return ret;
51     }
52 };