Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

public class Solution {
 public TreeNode sortedArrayToBST(int[] num) {
   return sortedArrayToBST(num, 0, num.length-1);
 }
 
 public TreeNode sortedArrayToBST(int[] num, int start, int end){
   if(start>end){
     return null;
   }
   int pivot = (start+end)/2;
   TreeNode root = new TreeNode(num[pivot]);
   root.left = sortedArrayToBST(num, start, pivot-1);
   root.right = sortedArrayToBST(num, pivot+1, end);
   return root;
 }
}

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