input: Write a python function to find all pairs in a list whose sum equals a given number.
  assert get_pairs([1, 2, 3, 4, 5], 5) == [[1, 4], [2, 3]]
  assert get_pairs([1, 2, 3, 4, 5, 6], 6) == [[1, 5], [2, 4]]
  assert get_pairs([1, 2, 3, 4], 7) == [[3, 4]]
  assert get_pairs([5, 5, 1, 1], 10) == [[5, 5]]
  assert get_pairs([], 5) == []
output: def get_pairs(lst, target):
      pairs = []
      seen = set()
      for num in lst:
          complement = target - num
          if complement in seen:
              pairs.append([complement, num])
          seen.add(num)
      return pairs