AdventOfCode programming puzzles 2021

In case you haven't seen it before...

https://adventofcode.com/2021/about

*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 a speed contest,
interview prep, company training, university coursework, practice problems,
or to challenge each other.

-gf-