All problems are from Kattis; each page links to its source.
You can write solutions in C++ (.cpp), Python (.py), or Java (.java).
Main goes in Main.java).From inside this folder, run ./test.py with the problem letter and your file:
./test.py A a.py ./test.py B b.cpp ./test.py C Main.java
The tester runs your program on every test case for that problem and reports how many pass. For the first test that fails, it shows the input, the expected output, and your output.