class Solution {
public:
TreeNode* sortedArrayToBST(vector<int>& nums) {
return helper(nums, 0 , (int)nums.size() - 1);
}
TreeNode* helper(vector<int>& nums, int left, int right) {
if (left > right) return NULL;
int mid = left + (right - left) / 2;
TreeNode *cur = new TreeNode(nums[mid]);
cur->left = helper(nums, left, mid - 1);
cur->right = helper(nums, mid + 1, right);
return cur;
}
};