A directory of a single problems must have:

One config.yml (add it by thaw init and fill in the information)
One checker.py.
At least one std.py or other kinds of standard code.
At least one gen.py or other kinds of data generator (except output-only problems).
At least one description file, like name_of_the_problem.zh-CN.md(or in other languages).

The checker.py could use the API by import thaw.checker.

Config

Checker

Standard program

Generator

If you use python, notice that although range() is a left closed and right open range, random.randint can get the two end points.

Description of the problem

Reference:

Codeforces notes to the author