Challenge7.kt

package challenge7

val pairs = { map: String -> map.replace("[", "").replace("]", "").split(",").map {
    val split = it.split("-")
    Pair(split.first().single(), split.last().single())
} }

val String.pairs get() = pairs(this)

val relatedWith = { relations: List<Pair<Char, Char>>, node: Char -> relations.filter { it.toList().contains(node) } }

fun List<Pair<Char, Char>>.relatedWith(node: Char) = relatedWith(this, node)

fun getCycles(relations: List<Pair<Char, Char>>, targetNode: Char, currentNode: Char, currentList: List<Char>): List<List<Char>> {
    if (targetNode == currentNode) {
        return listOf(currentList + targetNode)
    } else if (!currentList.contains(currentNode)) {
        return relations.relatedWith(currentNode).flatMap { getCycles(relations, targetNode, if (it.first == currentNode) it.second else it.first, currentList + currentNode) }
    }
    return emptyList()
}

val cyclesAround = { relations: List<Pair<Char, Char>> , targetNode: Char ->
    relations.relatedWith(targetNode).flatMap { getCycles(relations, targetNode, if (it.first == targetNode) it.second else it.first, listOf(targetNode)) }.filter { it.count() > 3 }
}

fun List<Pair<Char, Char>>.cyclesAround(targetNode: Char): List<List<Char>> = cyclesAround(this, targetNode)

val join = { cycle: List<Char> -> cycle.joinToString("").toUpperCase() }

val List<Char>.join get() = join(this)

val joined = { cycles: List<List<Char>> -> cycles.map { it.join } }

val List<List<Char>>.joined get() = joined(this)

fun findingCycles(targetNode: Char, map: String) = map.pairs.cyclesAround(targetNode).joined