def find_partners(aliensX, aliensY):
  if len(aliensX) <= 1:
    return aliensX, aliensY
  pivotX = aliensX[0]
  bY, pivotY, aY = partition(pivotX, aliensY)
  bX, _, aX = partition(pivotY, aliensX)

  bX, bY = find_partners(bX, bY)
  aX, aY = find_partners(aX, aY)
  return [*bX, pivotX, *aX], [*bY, pivotY, *aY]

def partition(pivot, aliens):
  b = []
  p = None
  a = []
  for alien in aliens:
    color = compare_aliens(pivot, alien)
    if color == "white":
      a.append(alien)
    elif color == "black":
      b.append(alien)
    else:
      p = alien
  return b, p, a

def compare_aliens(alien_x, alien_y):
    if alien_x == alien_y:
        return "green"
    elif alien_x < alien_y:
        return "white"
    else:
        return "black"

# Example usage
alienX = [1, 5, 2, 4, 3, 8, 6, 7]
alienY = [3, 7, 1, 8, 4, 5, 6, 2]

partners = find_partners(alienX, alienY)
print("Partners:", partners)