Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

class Solution {public:    void f(vector
     
       & v, int start, int end, TreeNode *&root){        if (start > end){            return;        }        int m = start + (end - start)/2;        if (!root){            root = new TreeNode(v[m]);            f(v,start,m-1,root->left);            f(v,m+1,end,root->right);        }    }    TreeNode *sortedArrayToBST(vector
      
        &num) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if (!num.size()){            return NULL;        }        TreeNode * root = NULL;        f(num,0,num.size() -1, root);        return root;    }};