input: Write a python function to remove duplicate elements from an array.
  assert removeDuplicates([2, 3, 4, 3, 2]) == [2, 3, 4]
  assert removeDuplicates([1, 1, 1, 1, 1]) == [1]
  assert removeDuplicates([10, 20, 10, 30, 20, 40]) == [10, 20, 30, 40]
output: def removeDuplicates(arr):
      seen = set()
      result = []
      for item in arr:
          if item not in seen:
              seen.add(item)
              result.append(item)
      return result