input: Write a function to delete all duplicates in a given list of numbers. The function should return a new list with all unique elements in the order they first appear. If the input list is empty, the function should return an empty list.
  assert deleteDuplicates([1, 2, 2, 3, 4, 4, 5])==[1, 2, 3, 4, 5]
  assert deleteDuplicates([5, 5, 5, 5, 5])==[5]
  assert deleteDuplicates([1, 2, 3, 4, 5])==[1, 2, 3, 4, 5]
  assert deleteDuplicates([])==[]
output: def deleteDuplicates(nums):
      seen = set()
      result = []
      for num in nums:
          if num not in seen:
              seen.add(num)
              result.append(num)
      return result