[LeetCode] Convert Sorted Array to Binary Search Tree

 1 /**
 2  * Definition for binary tree
 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     TreeNode *sortedArrayToBST(vector<int> &num) {
13         if (num.empty()) return NULL;
14         return sortedArrayToBST(num, 0, num.size() - 1);
15     }
16     TreeNode* sortedArrayToBST(vector<int> &num, int start, int last) {
17         if (start > last) return NULL;
18         
19         int half = (start + last) >> 1;
20         TreeNode* root = new TreeNode(num[half]);
21         root->left = sortedArrayToBST(num,start, half - 1);
22         root->right = sortedArrayToBST(num, half + 1, last);
23         
24         return root;
25     }
26 };