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EnglishWhat is Kattis (open.kattis.com)?
Updated
Kattis is an online programming problem archive where you can find thousands of programming problems to solve. If you're new, you register an account and start solving; the site tracks your score and places you on a ranklist. It's aimed at anyone who wants to practice competitive programming or algorithmic problem-solving, from beginners working through trivial problems to experienced solvers tackling hard ones.
What you can do on the site
The homepage presents the archive as its core feature: "Here you can find thousands of programming problems to solve." Beyond browsing and submitting solutions, the site surfaces several community views:
- Suggested problems — a curated list spanning difficulty levels, so you don't have to guess where to start.
- Ranklist — individual users ranked by score.
- Affiliations — organizations (mostly universities) ranked by combined score.
- Countries — countries ranked by combined score.
How difficulty and scoring work
Problems carry a point value that reflects difficulty. The suggested problems on the homepage show this spread clearly:
| Difficulty | Problem | Points |
|---|---|---|
| Trivial | Cetvrta | 1.3 pt |
| Trivial | Sum Squared Digits Function | 1.4 pt |
| Easy | Lawn Mower | 1.7 pt |
| Easy | Robot Protection | 2.2 pt |
| Medium | Bitmask | 3.2 pt |
| Medium | Elliptic Curve Point Multiplication | 3.7 pt |
| Hard | Flow Finder | 7.7 pt |
| Hard | Pipe Stream | 7.8 pt |
So a problem's point value is a rough proxy for how hard it is — higher points generally mean harder problems. Your total score accumulates across solved problems and determines your rank.
Who appears on the leaderboards
The ranklist shows individual solvers with their scores. At the time of the source data, the top entries were:
- Nick Wu — 18448.0
- Atli Fannar Franklín — 18313.0
- Doug Goodman — 15863.8
- Jeremy Lim — 14639.5
- Andreas Björklund — 12622.6
The affiliation ranking aggregates scores by institution:
| Rank | Affiliation | Score |
|---|---|---|
| 1 | National University of Singapore | 7,926.9 |
| 2 | Aarhus University | 5,857.8 |
| 3 | KTH Royal Institute of Technology | 5,682.2 |
| 4 | University of Iceland | 5,233.5 |
| 5 | University of Alberta | 4,223.9 |
And the country ranking aggregates by nation:
| Rank | Country | Score |
|---|---|---|
| 1 | United States | 9,673.7 |
| 2 | Canada | 8,792.9 |
| 3 | Singapore | 7,878.3 |
| 4 | Sweden | 7,592.6 |
| 5 | Iceland | 7,342.5 |
These three views let you compare yourself against individuals, schools, or countries depending on what motivates you.
How to get started
- Register an account — the site states that if you're new, you "just register and start solving."
- Pick a problem — use the suggested problems list to find one matching your level, or browse the archive.
- Solve and submit — your score updates as you solve problems, feeding into the ranklist.
The suggested problems list is the most direct entry point because it already sorts problems by difficulty, so you can start with a trivial 1.3-point problem and work upward rather than searching the full archive blind.
When Kattis is a good fit
Kattis suits you if you want a large, ranked problem archive with clear difficulty signals and social comparison through individual, school, and country leaderboards. It's less about structured courses and more about self-directed practice against a scored problem set. If you're preparing for competitive programming, working through algorithm topics, or representing a university, the affiliation and country rankings give the practice an extra dimension beyond your own score.