Advent of Code in Kotlin 2021 - Day 1

I look forward to Advent of Code every year. It's a series of fun, increasingly challenging puzzles for each day of December (until Christmas) that can be solved in any programming language.

There's 2 puzzles each day with the second one building on the first and typically a bit more challenging. On the 1st, the puzzles are usually pretty relatively straightforward and this year is no exception.

I'll post (some of) my solution here, starting with the first puzzle

For part 1, you are given a list of numbers (your puzzle input) and have to determine how many numbers are higher than the previous one. In most programming languages this can be solved with a for loop over the indices, but in Kotlin we can take advantage of windowed. Used on a list this gives us all pairs of consecutive numbers (a list of lists). Now we can apply a condition - the second number must be higher than the first - and count the number of matches. Done.

fun part1(measurements: List<Long>): Int = measurements
    .windowed(2)
    .count { it.last() > it.first() }

For part 2, you are asked to compare sums of consecutive numbers, so you're comparing 1st + 2nd + 3rd to 2nd + 3rd + 4th and so on. Here it might start to get messy with loops, but we can extend the windowing approach by taking windows with size 3 and then windows of size 2 of the windows. Meta.

fun part2(measurements: List<Long>): Int = measurements
    .windowed(3)
    .windowed(2)
    .count { it.last().sum() > it.first().sum() }

I'm pretty happy with that approach. Probably not particularly efficient, but on day 1 that's not yet a concern so readability trumps all.