input: Write a function to find the intersection of two arrays.
  assert intersection([1, 2, 3], [3, 4, 5]) == [3]
  assert intersection([10, 20, 30, 40], [20, 30, 50]) == [20, 30]
  assert intersection([5, 6, 7], [8, 9, 10]) == []
output: def intersection(arr1, arr2):
      return list(set(arr1) & set(arr2))