[LeetCode]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 *DFS(vector<int> &num,int left,int right)
    {
        if(right<left) return NULL;
        int mid=(left+right)>>1;
        TreeNode *root=new TreeNode(num[mid]);
        root->left=DFS(num,left,mid-1);
        root->right=DFS(num,mid+1,right);
        return root;
    }
    TreeNode *sortedArrayToBST(vector<int> &num) {
        return DFS(num,0,num.size()-1);
    }
};