109. 有序链表转换二叉搜索树

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 /**
10  * Definition for a binary tree node.
11  * struct TreeNode {
12  *     int val;
13  *     TreeNode *left;
14  *     TreeNode *right;
15  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
16  * };
17  */
18 class Solution 
19 {
20 public:
21     TreeNode* sortedListToBST(ListNode* head) 
22     {
23         vector<int> nums;
24         while(head)
25         {
26             nums.push_back(head->val);
27             head = head->next;
28         }
29 
30         if(nums.size() == 0) return NULL;
31         int l = 0,r = nums.size() - 1;
32         return slove(nums,l,r);
33     }
34 
35     TreeNode* slove(vector<int>& nums,int l,int r) 
36     {
37         int mid = (l + r)/2;
38         TreeNode* root = new TreeNode(nums[mid]);
39         if(mid != l) root->left = slove(nums,l,mid - 1);
40         else root->left = 0;
41 
42         if(mid != r) root->right = slove(nums,mid + 1,r);
43         else root->right = 0;
44 
45         return root;
46     }
47 };