tictactoe.kt

enum class Symbol(val text: String) { X("X"), O("O"), EMPTY("Tie") }
data class Slot(val x: Int, val y: Int, val symbol: Symbol)

fun main(args: Array<String>) {
    val input = args.getOrNull(0)

    if (input == null) {
        println("No input!")
        return
    }

    val result = input
        .toCharArray()
        .mapIndexed { i, c -> Slot(x = i % 3, y = i / 3, symbol = parseSymbol(c)) }
        .groupBy(Slot::symbol)
        .entries
        .filter { it.key != Symbol.EMPTY }
        .find { hasLinearSlope(it.value) }
        ?.key
        ?.text

    println(result ?: "Tie")
}

fun parseSymbol(char: Char): Symbol = when (char) {
    'X' -> Symbol.X
    'O' -> Symbol.O
    '#' -> Symbol.EMPTY
    else -> throw IllegalArgumentException("Bad input fam")
}

fun hasLinearSlope(slots: List<Slot>): Boolean = slots
    .combinationsOfThree()
    .any { slope(it.first, it.second) == slope(it.second, it.third) }

fun <T> List<T>.combinationsOfThree(): List<Triple<T, T, T>> =
    List(size = this.size) { i ->
        List(size = this.size - i) { j ->
            List(size = this.size - j) { h ->
                Triple(this[i], this[i + j], this[j + h])
            }
        }
    }.flatten().flatten().filter { it.first != it.second && it.second != it.third }

fun slope(slot1: Slot, slot2: Slot): Float =
    (slot1.y - slot2.y).toFloat() / (slot1.x - slot2.x).toFloat()