[108]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) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        return buildTree(num, 0, num.size()-1);    }        TreeNode* buildTree(vector<int> &num, int left, int right)    {        if(left > right)            return NULL;        int pos = (left + right) / 2;        TreeNode *root = new TreeNode(num[pos]);        root->left = buildTree(num, left, pos - 1);        root->right = buildTree(num, pos + 1, right);        return root;    }};