Leetcode-Convert Sorted Array to BST

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

Solution:

 /**
  * 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) {
         if (num.length==0)
             return null;

         int end = num.length-1;
         TreeNode root = sortedArrayToBSTRecur(num,0,end);
         return root;
     }

     public TreeNode sortedArrayToBSTRecur(int[] num, int head, int end){
         if (head==end){
             TreeNode root = new TreeNode(num[head]);
             return root;
         }

         if (head+1==end){
             TreeNode root = new TreeNode(num[end]);
             TreeNode child = new TreeNode(num[head]);
             root.left = child;
             return root;
         }

         //Calculate the median index.
         int len = end-head;
         int mid = head + len/2 + len%2;
         TreeNode root = new TreeNode(num[mid]);
         TreeNode leftChild = sortedArrayToBSTRecur(num,head,mid-1);
         TreeNode rightChild = sortedArrayToBSTRecur(num,mid+1,end);
         root.left = leftChild;
         root.right = rightChild;
         return root;
     }
 }