input: from typing import List
  
  def split_array(nums: List[int]) -> List[int]:
      """
      Given an array of unique integers with a 1-based index, you need to split it into two separate arrays, arr1 and arr2, using a number of operations equal to the length of nums. Start by adding nums[1] to arr1, and then nums[2] to arr2. For each subsequent element:
  
      Append nums[i] to arr1 if its last item is greater than the last item of arr2, else append nums[i] to arr2.
      The final array should be the concatenation of arr1 followed by arr2. For instance, with arr1 as [1,2,3] and arr2 as [4,5,6], the final array would be [1,2,3,4,5,6].
  
      Return this combined array.
  
      Examples:
      >>> nums = [2,1,3]
      [2,3,1]
      >>> nums = [5,4,3,8]
      [5,3,4,8]
  
      Constraints:
      3 <= n <= 50
      1 <= nums[i] <= 100
      Each element in nums is unique.
      """
output:     arr1 = [nums[0]]
      arr2 = [nums[1]]
      for num in nums[2:]:
          if arr1[-1] > arr2[-1]:
              arr2.append(num)
          else:
              arr1.append(num)
      return arr1 + arr2