Fish Farm Counter - AOC - Day 6

fishFarmCounter.kt

class FishFarmCounter(input: String) {
    private val fish = LongArray(NEWBORN_MAX_SEED + 1)

    init {
        input.split(",")
            .filter { it.trim().isNotEmpty() }
            .map { it.trim().toInt() }
            .forEach {
                fish[it]++
            }

    }

    private fun plusDay() {
        val parentsCount = fish[0]
        fish.takeLast(NEWBORN_MAX_SEED)
            .onEachIndexed { index, count ->
                fish[index] += count
                fish[index + 1] -= count
            }
        fish[NEWBORN_MAX_SEED] += parentsCount
        fish[MAX_SEED] += parentsCount
        fish[0] -= parentsCount
    }

    fun plusDays(days: Int): Long {
        for (i in 0 until days) {
            plusDay()
        }
        return fish.sum()
    }
}

// and the calling code
fun main() {
    fun part2(input: List<String>): Long {
        return FishFarmCounter(input[0]).plusDays(MORE_DAYS)
    }

    // test if implementation meets criteria from the description, like:
    val testInput = readInput("day6/Example_test")
    val part2 = part2(testInput)
    check(part2 == 26984457539L)

    val input = readInput("day6/Example")
    println("******* PART 2: ${part2(input)} *******")
}