text: def arr_pair_sum(arr, k):
      # edge case
      if len(arr) < 2:
          return
      # set for tracking
      seen = set()
      output = set()
  
      for num in arr:
          target = k - num
  
          if target not in seen:
              seen.add(num)
          else:
              output.add((min(num, target), max(num, target)))
      return len(output)
  
  
  print(arr_pair_sum([1, 3, 2, 2], 4))
  