Hi,

I am trying to solve this problem from atcoder : B — LRUD Game. After reading the editorial and this https://codeforces.com/blog/entry/66849#comment-510066, I still do not understand the solution and have the following 2 questions:

1. why we need to process all moves by both players backwards?
2. When processing backwards, other than the last move by the 2nd player, we need to first do updates based on the 2nd player's moves, then the 1st player's moves. Doing it the opposite yields a wrong answer.

Can some one help me understand the above 2 key ideas?

This is my AC submission after reading other people's submission: submission link.

Thanks!