input: Write a python function to check if there are any two numbers in a list that add up to a given sum.
  assert two_sum([1, 3, 7, 4, 5], 12) == True
  assert two_sum([1, 2, 3, 4, 5], 10) == False
  assert two_sum([0, -1, 2, -3, 1], -2) == True
  assert two_sum([10, 20, 30, 40, 50], 60) == True
output: def two_sum(nums, target):
      seen = set()
      for num in nums:
          if target - num in seen:
              return True
          seen.add(num)
      return False