input: Write a function to determine if there exists any pair of numbers in the given list that sum up to the target number. If such a pair exists, return True; otherwise, return False. If the list is empty, return True.
  assert check_sum([1, 2, 3, 4], 5)==True
  assert check_sum([1, 2, 3, 4], 8)==False
  assert check_sum([1, 1, 1, 1], 2)==True
  assert check_sum([], 10)==True
output: def check_sum(nums, target):
      if not nums:
          return True
      seen = set()
      for num in nums:
          if target - num in seen:
              return True
          seen.add(num)
      return False