DragonGorynych.kt

data class Variant(val step: Int, val Nheads: Int, val Mtails: Int, val comment: String = "", val prev: Variant? = null)

fun main(args: Array<String>) {
    val variants = mutableListOf<Variant>()
    variants.add(Variant(step = 0, Nheads = 3, Mtails = 1))
    var i = 0
    val max = 10
    var result: Variant? = null
    val isSwordBroken = true
    while (variants[i].step <= max) {
        val current = variants[i]
        val extraTail = if(isSwordBroken && (current.step + 1) % 3 == 0) 1 else 0
        // 1 tail produces 2 tails
        if(current.Mtails >= 1) {
            val next = Variant(current.step + 1, current.Nheads, current.Mtails + 1 + extraTail, "1 tail", current)
            if (checkVariant(next, extraTail)) {
                result = next
                break
            }
            variants.add(next)
        }
        // 2 tails produces 1 head
        if (current.Mtails >= 2) {
            val next = Variant(current.step + 1, current.Nheads + 1, current.Mtails - 2 + extraTail, "2 tails", current)
            if (checkVariant(next, extraTail)) {
                result = next
                break
            }
            variants.add(next)
        }
        // 1 head produces 1 head
        if(isSwordBroken && current.Nheads >= 1) {
            val next = Variant(current.step, current.Nheads, current.Mtails + extraTail, "1 heads", current)
            if (checkVariant(next, extraTail)) {
                result = next
                break
            }
            variants.add(next)
        }
        // 2 heads produces nothing
        if(current.Nheads >= 2) {
            val next = Variant(current.step + 1, current.Nheads - 2, current.Mtails + extraTail, "2 heads", current)
            if (checkVariant(next, extraTail)) {
                result = next
                break
            }
            variants.add(next)
        }
        i++
    }
    while (result != null) {
        println(result.let { Variant(it.step, it.Nheads, it.Mtails, it.comment) })
        result = result.prev
    }
}

fun checkVariant(variant: Variant, extraTail: Int): Boolean {
    return variant.Nheads == 0 && variant.Mtails == 0 && extraTail == 0
}