import java.io.*
import kotlin.math.*
import kotlin.system.*

fun main() {
    var state = File("input_actual.txt").readLines()
    state.forEach { println(it) }

    do {
        println("\ntransform\n")
        val new = transform(state)
        new.forEach { println(it) }
        val isChanged = new != state
        state = new
    } while (isChanged)

    println(state.sumBy { it.count { it == '#' } })
}

fun transform(old: List<String>) = old.mapIndexed { y, line ->
    line.mapIndexed { x, char ->
        val neighbours = old.subList(max(y - 1, 0), min(y + 1, old.lastIndex) + 1).sumBy {
            it.substring(max(x - 1, 0)..min(x + 1, line.lastIndex)).count { it == '#' }
        }.let { if (char == '#') it - 1 else it }

        when {
            char == 'L' && neighbours == 0 -> '#'
            char == '#' && neighbours >= 4 -> 'L'
            else -> char
        }
    }.joinToString("")
}