Compete with friends on LeetCode-style problems
Practising with friends works better with a scoreboard. Send a friend a private code, and you both get the same interview-style problem, language and clock in a live 1v1 duel.
How to challenge a friend
- Both of you create a free DuelCoder account with email or Google.
- Open Play, choose Friend challenge, pick a language and create a private code.
- Send the code to your friend. They enter it to join your duel.
- You both get the same randomly assigned problem on a 35-minute clock.
- The first solution that passes the hidden tests wins. Friend challenges never change either player's rating.
Why duel instead of solving side by side
- It feels like an interview: a fixed clock and someone else racing you.
- It is a fair comparison: same problem, same language, same time limit.
- Nobody argues about whether a solution counts. Hidden tests on the server decide.
- No screen sharing or honour system. You each code in your own browser.
What you will practise
Duels use the Blind 75, the best-known list of coding-interview problems, across 18 topics: arrays and hashing, two pointers, sliding window, stacks, binary search, linked lists, trees, tries, heaps, backtracking, graphs, dynamic programming, greedy, intervals, math and bit manipulation. Each problem has a public page with the approach, complexity and common pitfalls.
When you are ready for strangers
Ranked Standard and Speed queues match you with players at your Skill Rating. Your rank is confirmed after 5 rated duels, and seasons give everyone a fresh race for the leaderboard.
Not affiliated with LeetCode
DuelCoder is independent. “LeetCode-style” describes the problem format: a function to implement, sample tests to run and hidden tests to pass. DuelCoder's statements and tests are written separately.
Frequently asked questions
Does a friend challenge change my rating?
No. Friend challenges are unrated for both players.
Do both players need an account?
Yes. Accounts are free, and you can sign up with email or Google.
Can we pick the problem?
No. The problem is assigned at random when the duel starts, so neither player can prepare it. To practise a specific problem, open it in practice mode.
Do we have to use the same language?
Yes. The host picks the language and both players code in it. TypeScript, JavaScript, Python and C++ are available.