Anyone has any document or knowledge about performing reverse operation in segment tree by using treap ? There is a problem in Codechef that is required to do it, treap is mentioned but isn't explained in the tuttorial. Link to problem: http://www.codechef.com/problems/PALINDR

What could be the reason of problem that I cant see the CAPTCHA picture when trying to register ?

Hi, As you know practice tasks are published in the last week, if you know solutions can you share some hints, thanks in advance.

is 'feedback system' used at baltic olympiad.. anybody knows ?