```
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* helper(const vector<int> &A, int low, int high)
{
if (high < low)
return nullptr;
int mid = (low+high+1)/2;
TreeNode *node = new TreeNode(A[mid]);
node->left = helper(A, low, mid-1);
node->right = helper(A, mid+1, high);
return node;
}
TreeNode* sortedArrayToBST(vector<int>& nums) {
int len = nums.size();
//if (len == 0)
// return nullptr;
return helper(nums, 0, len-1);
}
};
```