Frequently asked questions about CodeKairo Battles

Plain answers about hosting and entering tournaments on CodeKairo Battles: cost, verification, who may enter, the two formats, languages, scoring and what counts on your CodeKairo profile.

Running a tournament

How much does it cost to host a tournament?
Nothing. Hosting on CodeKairo Battles is free: the organization, drafting and publishing tournaments, the judge, the bracket, the scoreboard and the results. Players need only a free CodeKairo account.
Who can host a tournament?
Anyone signed in can create an organization — a college or university, a student club or chapter, a company or a community — and draft tournaments straight away. A tournament becomes public only once CodeKairo has verified its organization, which happens once, before the first public event; the official name and website make that quick.
Can I limit a tournament to students of my college?
Yes. Each tournament can be open to anyone, limited to email domains such as college.edu (subdomains count, look-alike domains do not), gated by an invite code, set to need your approval for every registration — or any combination of these — with an optional cap on places.
Which problems can I use?
Up to 15 problems chosen from the CodeKairo catalogue of about 600, each with hidden tests and starter code in 13 languages. Players see only how many problems there are until the start. Writing your own problems is not supported yet.
What do I see about the people who register?
Their CodeKairo name and the domain of their email address — enough to check that they are eligible — never the address itself.
How do I enter the teams for an ICPC-style contest?
Paste the list: one team per line, the team's name and then each member's CodeKairo email or username, separated by commas — a pasted spreadsheet works too. Up to 500 teams go in one upload; nothing is saved unless the whole list is clean, and every problem is reported with its line number.

Entering and playing

Do I need a separate account for Battles?
No. Battles uses your CodeKairo account: sign in on Battles with email, Google or GitHub, or arrive already signed in from codekairo.com. An account created on Battles works on CodeKairo too, and both are free.
How do I enter a knockout?
Open the tournament and register before registration closes. Depending on the organizer you may need an email address on their domain, an invite code or their approval. Then check in during the hour before the start — only players who checked in are seeded.
How do I join an ICPC-style contest?
You do not register yourself: the organizer enters every team and names each member by CodeKairo email or username. Sign in with that account and the contest is listed under your tournaments.
Which languages can I use?
All 13 the CodeKairo judge accepts: JavaScript, TypeScript, Python, Java, C++, C, C#, Go, Kotlin, Swift, Rust, PHP, Ruby.
Do tournament solves count on my CodeKairo profile?
Yes. An accepted submission in a tournament is an ordinary CodeKairo submission: it counts toward your solved problems, activity heatmap, streak and roadmap stages, and pays XP the first time you solve that problem. The problem is marked as solved in a tournament, and your profile lists every tournament you played with where you finished.

1v1 knockouts

How are players seeded in a knockout?
By CodeKairo rating, highest first; players with the same rating are ordered by who registered first. Only players who checked in during the hour before the start are seeded.
What if the number of players is not a power of two?
The bracket is the next power of two and the places beyond the field are byes, which go to the top seeds. No first-round match is two byes, and the top two seeds can only meet in the final.
Which problem is each match played on?
Every match of a round plays the same problem: round one the organizer's first problem, round two the second, and so on — from the first again if there are more rounds than problems.
What happens if a match runs out of time?
Whoever passed more hidden test cases wins; if that is level, whoever reached that number first; if neither submitted, the better seed. A player who never submitted loses to one who did.
Can I see how my opponent is doing?
Yes. The match room shows both players' best number of hidden tests passed, updated every few seconds. Neither player sees the other's code.
When does my next match start?
A minute after both of its players are known — a player who wins early waits for the other side of the bracket to finish.

ICPC-style contests

How is an ICPC-style scoreboard ranked?
By problems solved, then by total penalty time, then by who reached their last solve first. Teams level on all three share a rank.
How is penalty time counted?
For each solved problem: the minutes from the start to its first accepted submission, plus 20 minutes for every rejected attempt before it. An unsolved problem costs nothing, and later submissions on a solved problem are ignored.
Does a compile error count as a wrong attempt?
No. A compile error, or the judge failing to run the code, costs no penalty and is not an attempt. Wrong answer, time limit, runtime error and memory limit are.
What is the scoreboard freeze?
For the last part of the contest — an hour by default, set by the organizer, or none — the public board stops showing other teams' results: their attempts appear as pending. After the end, the organizer reveals the final standings.
How big can a team be?
The organizer sets it to one, two or three members. Each member signs in with their own CodeKairo account and works in the same contest room.
How long is a contest?
As long as the organizer sets it, from 10 minutes to 12 hours; three hours is the default. Every team starts and finishes on the same clock.