My Missing Pages solution (Practice 8/21/2014)

pages.py

def pagesTaken(N, P):
	original_p = P

	# adjust P to be less than N/2
	if P > N/2:
		P = N - P + 1

	# if even, move back a page
	if P % 2 == 0:
		P -= 1
		
	# Note: At this point, P is the smallest page on the same page as original_p

  # Here's a neat Python 3 thing: set literals. I'm actually doing a set difference here. 
  # I'm creating a set of all elements on a single page, and then removing the page that 
  # was already provided, since we're not supposed to print that one.
	removed_pages = { P, P + 1, N - P + 1, N - P } - { original_p }
	
	# Lastly, sort for good measure
	return sorted(removed_pages)

while True:
	line = input()
	if line == '0':
		break

	N, P = map(int, line.split())
	
	# Sorry this is jumbled, but it works.
	print(' '.join(map(str, pagesTaken(N, P))))

  # I'll split it up here, so you know what's going on, but I haven't tested this:
  pages_taken = pagesTaken(N, P) # This is a list of ints (from the sorted call)
  str_pages_taken = map(str, pages_taken) # Now its a "map" object of strings
  output = ' '.join(str_pages_taken) # Squishing the strings together by ' '. So ['1', '2'] becomes '1 2'
  print(output) # Print it out.