108. Convert Sorted Array to Binary Search Tree

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

 

public TreeNode sortedArrayToBST(int[] nums) {
  if (nums.length == 0) return null;
  TreeNode head = helper(nums, 0, nums.length - 1);
  return head;
}
public TreeNode helper(int[] num, int low, int high) {
  if (low > high) 
    return null;
  int mid = low + (high - low) / 2;
  TreeNode node = new TreeNode(num[mid]);
  node.left = helper(num, low, mid - 1);
  node.right = helper(num, mid + 1, high);
  return node;
}