input: Write a function to find pairs of elements in an array that add up to a given sum.
  assert findElements([3, 5, 2, -4, 8, 11], 7) == [[3, 4], [11, -4]]
  assert findElements([1, 2, 3, 4, 5, 6], 10) == [[4, 6]]
  assert findElements([0, 0, 0, 0], 0) == [[0, 0], [0, 0], [0, 0]]
  assert findElements([1, 1, 1, 1], 2) == [[1, 1], [1, 1], [1, 1]]
output: def findElements(arr, target_sum):
      pairs = []
      seen = {}
      for num in arr:
          complement = target_sum - num
          if complement in seen:
              pairs.append([complement, num])
          seen[num] = True
      return pairs