"You can reverse N contiguous items in V at a time." When you reverse elements 1-5 you're assuming N == 5. When you reverse elements 1-4 you're assuming N ==

"You can reverse N contiguous items in V at a time." When you reverse elements 1-5 you're assuming N == 5. When you reverse elements 1-4 you're assuming N == 4. I think this violates the problem statement that N is fixed.