The CSES Problem Set is a collection of competitive programming practice problems.
The goal of the project is to create a comprehensive high quality problem set for learning competitive programming. The current collection has 200 problems, and new problems will be gradually added.
You can solve problems in several languages, including C++, Java, and Python. More information about available languages is here.
After solving a problem, you can view the solutions by other users and try to hack them by giving a test case where the solution fails. If your hack is successful, the new test case will be added to the test data and all submissions will be regraded.
The problem set has been designed so that you can use it together with recent competitive programming books, listed here. The books discuss techniques and ideas that are useful when solving the problems.
The license of the problem set is Creative Commons BY-NC-SA.
Do you have ideas on how to improve the problem set? You can always send a message to ahslaaks@cs.helsinki.fi (Antti Laaksonen).