1v1 coding battles: you, a rival and the same problem
A coding battle on DuelCoder is a race to the first correct solution. You and one opponent get the same problem, the same language and the same clock, and the server decides who solved it first.
How a 1v1 coding battle works
- Queue: pick Standard or Speed and the language you want to code in.
- Match found: DuelCoder pairs you with a rival close to your Skill Rating.
- Solve: you both get the same randomly assigned problem. Run your code against the sample tests as often as you like.
- Submit: your solution runs against hidden tests on the server, inside an isolated sandbox.
- Result: the first accepted solution wins. If nobody solves it before the clock ends, the duel is a draw. Your rating updates only after the server's verdict.
Standard, Speed and friend battles
| Mode | Clock | Rating |
|---|---|---|
| Ranked Standard | 35 minutes | Standard Skill Rating |
| Ranked Speed | 15 minutes | Speed Skill Rating (separate) |
| Friend challenge | 35 minutes | No rating change |
| Practice | No clock | No rating change |
Fair by design
- Both players get the same problem, the same language and the same clock.
- The problem is assigned at random when the battle starts, so nobody can prepare it in advance.
- Matchmaking uses a Glicko-2 Skill Rating, so you usually meet someone at your level.
- Solutions are judged only on the server, against hidden tests, with no network access.
- Nothing you can buy changes matchmaking, judging or rating.
Ranks and seasons
Every rated battle moves your Skill Rating. Bronze, Silver, Gold, Platinum and Diamond each have three divisions, 50 SR apart, followed by Master and Grandmaster. Your first 5 rated battles are placement: you see an estimated tier until your rank is confirmed.
Seasons reset the race for the top of the leaderboard, not your skill. Standard and Speed keep separate ratings, so a fast solver and a careful solver can both climb.
What you need
- A free account, created with email or Google.
- One language you are comfortable in: TypeScript, JavaScript, Python and C++.
- Basic data structures. If you are rusty, warm up on the Blind 75 in practice mode first.
Frequently asked questions
Are 1v1 coding battles free?
Yes. Ranked battles, friend challenges and practice are free, and paying never changes matchmaking, judging or rating.
What happens if both players solve the problem?
The first solution the server accepts wins. Submitting a wrong answer does not end your battle; you can fix it and submit again before the clock ends.
How long is a coding battle?
Standard battles have a 35-minute clock and Speed battles 15 minutes. A battle ends early as soon as one player's solution is accepted.
Can I practise before playing ranked?
Yes. Practice mode has every problem with sample tests and hints, with no clock and no rating change.