So.. Do you (all of you who says that input format is correct) mean that books are stored in a way that the last page is the leftmost one? If so than it's not surprising that the solution which swaps numbers of the books gets AC.

Hah, I wasn't familiar with this particular trick, but I've done enough of the "simple" problems on Timus now to know that many problems derive their difficulty not from the underlying algorithm, but in correctly understanding problem statements which are sometimes tricky, ambiguous, or rely on unstated assumptions (like this one, assuming how people "normally" put books on shelves, and which side of the book contains the first page).

So I'm learning to always ask "what's the catch?" and got AC first time on this one (after initial WA on many other "simple" problems).   So solving Timus problems is successfully training me to read problems very carefully!

This problem can be solved fast, if you'll try not to consider common solution, but only this ( there is some useful limits in statement, also order is very convenient  ) case.
Small hint, that I promised: Imagine a big-length wall, like in old platformers, where segments are vertical levels and segment's coords are horizontal coords.
Example:
4
2 10
2 3
5 7
6 7

00000011000
00110111000
00111111111
1 are bricks in our wall.

Edited by author 14.03.2014 11:03