Advent of Code 2015 in Kotlin, done at a slow pace in 2022

This is done together with a few friends and colleagues who want to use the AoC problems to improve their coding proficiency. In my case, I am using these problems to practice Kotlin while I learn it.

A remark on Kotlin for each “day”:

• 01: when() control structure (or expression) is nice to have – also appeared in python 3.10
• 02: extensions functions combine well with a “functional programming” style
• 03: companion object is Kotlin’s way of grouping “constant” or “static” members of a class
• 04: single-line fun definitions with = and expression if may help with short, readable code
• 05: maybe extension functions should be scope-restricted to avoid accidental misuse?
• 06: during class inheritance, explicit use of the override keyword is mandatory
• 07: testing for null can be chained with “elvis operators”
• 08: beware of Regex expressions containing backslashes or double quotes, even in “raw” strings
• 09: nullability checks matter, notably for map elements! (and can cause headaches when absent…)