Convert Sorted Array to Binary Search Tree

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

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode *sortedArrayToBST(vector<int> &num) 
    {
        return getBSTtree(num,0,num.size()-1);
    }
    TreeNode* getBSTtree(vector<int> & num, int left,int right)
    {
        if(left>right)
            return NULL;
        TreeNode *root;
        if(right-left+1==1)
        {
            root=new TreeNode(num[left]);
            return root;
        }
        int mid=(left+right)/2;
        root=new TreeNode(num[mid]);
        root->left=getBSTtree(num,left,mid-1);
        root->right=getBSTtree(num,mid+1,right);
    }
};