"Moscow SU team Red Panda has found the winning ways again, this time thanks to being the only team to solve problem I — and doing it in the beginning of the third hour of the contest, which is quite unusual for a problem with only one solver" — I remember one case of AMPPZ which is Polish stage of ICPC, where there was one problem that:
1) was solved by only one team
2) this team solved it in the beginning of second hour (something like 1:15)! AND
3) this was unofficial team from high school!

(inb4, this task didn't require knowledge of a very specific trick or knowledge or something that only this team saw before)