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

int len = num.size();

if(!len)return NULL;

return mySortedArrayToBST(num,0,len-1);

}

TreeNode *mySortedArrayToBST(vector<int> &num,int start,int end)

{

if(start>end)return NULL;

int mid = (start+end)/2;

TreeNode * parent = new TreeNode(num[mid]);

parent->left = mySortedArrayToBST(num,start,mid-1);

parent->right = mySortedArrayToBST(num,mid+1,end);

}

};