input: Write a python function to find pairs of numbers in a list that add up to a given sum.
  assert twoSum([2, 3, 4, 5, 7, 10], 5) == [(3, 2)]
  assert twoSum([1, 2, 3, 4, 5, 6], 7) == [(6, 1), (5, 2), (4, 3)]
  assert twoSum([0, -1, 2, -3, 1], -2) == [(-1, -1), (-3, 1)]
output: def twoSum(nums, target):
      pairs = []
      seen = set()
      for num in nums:
          complement = target - num
          if complement in seen:
              pairs.append((num, complement))
          seen.add(num)
      return pairs