CSES Problem Set
Solve 400 classic algorithm problems sorted by topic
The CSES Problem Set is a collection of 400 algorithm problems. You read a problem, write a program that reads from standard input and writes to standard output, and submit it to be judged. Problems are grouped by topic, such as sorting and searching, dynamic programming, graphs, range queries, trees, math, strings and geometry.
Free · Browser · Intermediate
About CSES Problem Set
It trains the core techniques of competitive programming in a clear order. It suits learners who want a structured path, and it pairs well with competitive programming books. After you solve a problem, you can read other people's solutions and try to break them with a test case.
You can use C++, Java, Python and other languages. It is free, and Antti Laaksonen runs it at the University of Helsinki.
On Breakpoint since 23 Oct 2026.