You all might have seen that we can see our friend group's rank list on codeforces in real-time. It makes me wonder how this feature is implemented at the BackEnd? I surely know that they initialize these customised lists at the time of registration because we can see registered friends too. Can anyone from the tech-team or anyone who has an idea help me know this. Do they keep a sorted-set kind of thing to implement this friends-ranklist and also is the score updation event-driven? MikeMirzayanov