val fish = File("src/day6/input.txt").readLines()[0].split(",").map { it.toInt() }

    val fish = File("src/day6/input.txt").readLines()[0].split(",")
        .map { it.toInt() }.groupingBy { it }.eachCount()

fun solve(input: List<Int>, days: Int): BigInteger {
    var fish = input
        .groupingBy { it }
        .eachCount()
        .mapValues { it.value.toBigInteger() }
        .toMutableMap()
    for (day in 1..days) {
        fish = fish.mapKeys { (9 + it.key.minus(1)) % 9 }.toMutableMap()
        fish[6] = (fish[6] ?: 0.toBigInteger()).add(fish[8] ?: 0.toBigInteger())
    }
    return fish.values.reduce { a, b -> a.add(b) }

fun solve(input: Map<Int, Int>, days: Int): BigInteger {
    val fish = Array(9) { (input[it] ?: 0).toBigInteger() }
    (1 until days).forEach { fish[(it + 7) % 9] += fish[it % 9] }
    return fish.reduce { a, b -> a + b }