input: Write a python function to calculate the sum of unique elements in a provided array.
  assert sum_unique([1,2,3,1,1,4,5,6],8) == 21
  assert sum_unique([1,10,9,4,2,10,10,45,4],9) == 71
  assert sum_unique([12,10,9,45,2,10,10,45,10],9) == 78
output: def sum_unique(arr, n):
      return sum(set(arr))