input: Write a function to determine if there are any two numbers in a given list that add up to a specified number. If there are such numbers, return True; otherwise, return False. If the list is empty, return False.
  assert two_sum([1, 2, 3, 4], 7)==True
  assert two_sum([1, 2, 3, 4], 8)==False
  assert two_sum([10, 20, 30, 40], 50)==True
  assert two_sum([1, 3, 5, 7, 9], 14)==True
  assert two_sum([], 9)==False
output: def two_sum(nums, target):
      seen = set()
      for num in nums:
          complement = target - num
          if complement in seen:
              return True
          seen.add(num)
      return False