day1.md

Day 1: Sonar Sweep

[source]

The elves lost Santa's keys to the depths, and we need to use a submarine to find and retrieve them.

Part 1

Given a list of depths proceeding outward from your submarine, find how many times the depth measurement increases from the previous value.

A Kotlin sequence .zipWithNext() made quick work of this. It maps a value and it's next value, allowing me to quickly find the diff of the two values.

    File(inputFile).readLines().asSequence()
        .map { it.toInt() }
        .zipWithNext { a, b -> b - a }
        .count { it > 0 }
        .apply { println(this) }

Part 2

Instead of taking the values provided, instead consider the sums for a 3-measurement sliding window before looking for increasing values.

Again, Kotlin sequences have us covered with the .windowed() function. By giving it a size of 3 I instantly get exactly what we want, sliding windows of 3 values that can be easily summed.

    File(inputFile).readLines().asSequence()
        .map { it.toInt() }
        .windowed(3)
        .map { it.sum() }
        .zipWithNext { a, b -> b - a }
        .count { it > 0 }
        .apply { println(this) }