Advent of Code is an Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like. People use them as interview prep, company training, university coursework, practice problems, a speed contest, or to challenge each other.
Advent of Code is an annual online coding event that takes place in December, leading up to Christmas. It was created by Eric Wastl and first introduced in 2015. The event consists of a series of small programming puzzles released daily from December 1st until December 25th. Each day typically features two puzzles: the second puzzle is unlocked after solving the first.
You don't need a computer science background to participate - just a little programming knowledge and some problem solving skills will get you pretty far. Nor do you need a fancy computer; every problem has a solution that completes in at most 15 seconds on ten-year-old hardware.