/**

* Definition for binary tree

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

* TreeNode(int x) { val = x; }

* }

*/

public class Solution {

public TreeNode sortedArrayToBST(int[] num, int start, int end){

if(num==null || num.length==0 || start>end){

return null;

}

if(start==end){

TreeNode tn = new TreeNode(num[start]);

tn.left = null;

tn.right = null;

return tn;

}

int mid = start + (end-start)/2;

TreeNode tn = new TreeNode(num[mid]);

tn.left = sortedArrayToBST(num,start,mid-1);

tn.right = sortedArrayToBST(num,mid+1,end);

return tn;

}

public TreeNode sortedArrayToBST(int[] num) {

// Start typing your Java solution below

// DO NOT write main() function

return sortedArrayToBST(num,0,num.length-1);

}

}