input: Write a python function to determine if there are two numbers in an array that add up to a given sum.
  assert twoSum([1, 2, 3, 4, 5], 9) == True
  assert twoSum([1, 2, 3, 4, 5], 10) == False
  assert twoSum([10, 20, 30, 40, 50], 70) == True
  assert twoSum([0, -1, 2, -3, 1], -4) == False
output: def twoSum(arr, target):
      seen = set()
      for num in arr:
          if target - num in seen:
              return True
          seen.add(num)
      return False