Sorted Array to Binary Search Tree - Java

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