https://adventofcode.com/2025

Day1Part1.kt

fun main() {
    input.let(::calculatePassword)
        .let(::println)
}

fun calculatePassword(input: List<String>): Int =
    input.map(::parseMoveDelta)
        .scan(50) { position, delta ->
            normalize(position + delta)
        }
        .count(0::equals)

fun parseMoveDelta(text: String): Int {
    val amount = text.drop(1).toInt()
    return when (text.first()) {
        'L' -> -amount
        'R' -> amount
        else -> error("Unexpected move instruction")
    }
}

const val start = 0

const val end = 100

// Forces position to stay within [`start`, `end`] range
// which represents closed dial
fun normalize(position: Int): Int {
    var normalized  = position
    while (normalized  < start) normalized  += end
    while (normalized  >= end) normalized  -= end
    return normalized
}