input: def find_pair(lst, target):
      """ Find a pair of numbers in the given list that add up to the target number.
  
      >>> find_pair([1, 2, 3, 4, 4, 5, 6], 8)
      [3, 5]
      """
output:     seen = set()
      for num in lst:
          complement = target - num
          if complement in seen:
              return [complement, num]
          seen.add(num)
      return []