At Codeforces Round #833 (Div. 2)
There is a case of cheating in the problem B A solution is available during the contest on YouTube https://youtu.be/0x9kKxfqLr8
Matching solutions:- https://codeforces.net/contest/1748/submission/180650292
https://codeforces.net/contest/1748/submission/180650184
https://codeforces.net/contest/1748/submission/180649269
https://codeforces.net/contest/1748/submission/180646072
https://codeforces.net/contest/1748/submission/180646346
https://codeforces.net/contest/1748/submission/180646263
