input: Write a function to take as input two array of integers and swap their elements.
  assert swap([3, 5, 6, 9], [2, 4, 7, 8])==None
  assert swap([1, 2, 3], [4, 5, 6])==None
  assert swap([10, 20], [30, 40])==None
  assert swap([1], [2])==None
  assert swap([], [])==None
output: def swap(arr1, arr2):
      arr1[:], arr2[:] = arr2[:], arr1[:]