1 class Solution {

 2 public:

 3     TreeNode* sortedArrayToBST(vector<int>& nums) {

 4         if(nums.size() == 0) return NULL;

 5         return build_BST(nums,0,nums.size()-1);

 6     }

 7     TreeNode* build_BST(vector<int>& nums,int low,int high){

 8         if(low > high) return NULL;

 9

10         int mid = (low + high) / 2;

11         TreeNode* root = new TreeNode(nums[mid]);

12         root->left = build_BST(nums,low,mid-1);

13         root->right = build_BST(nums,mid+1,high);

14         return root;

15     }

16 };