[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);

    }

};