UVa Online Judge
Solve classic contest problems and get judged on hidden tests
This judge holds a large archive of classic algorithm problems, more than 4,300 of them. You read a problem, write a program that reads the input and prints the exact output, and submit it. The judge runs your code on hidden tests and tells you if it is accepted, wrong or too slow.
Free · Login needed · Browser · Intermediate
About UVa Online Judge
It trains core competitive programming skills: careful input handling, data structures, graph search, dynamic programming and math. Many problems come from old contests, so it suits learners who already know one language well and want steady practice.
The site runs in the browser and is free, but you need an account to submit. Miguel Ángel Revilla started it at the University of Valladolid in Spain in 1995. It accepts C, C++, Java, Pascal and Python.