Convert Sorted Array to Binary Search Tree

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

#include<iostream>#include<vector>using namespace std;struct TreeNode {int val;TreeNode *left;TreeNode *right;TreeNode(int x) : val(x), left(NULL), right(NULL) {}};TreeNode * CreatBST(vector<int> &num, int first, int last){if (first > last)return NULL;int mid = (first + last) / 2;TreeNode* curnode = new TreeNode(num[mid]);curnode->left = CreatBST(num, first, mid - 1);curnode->right = CreatBST(num, mid + 1, last);return curnode;}TreeNode *sortedArrayToBST(vector<int> &num) {if (num.empty())return NULL;return CreatBST(num, 0, num.size() - 1);}