Day 10 part 2

Day10.kt

package day10

import java.nio.file.Files
import java.nio.file.Path
import kotlin.system.measureTimeMillis


object Day10b {
    val mapScore = mapOf(
        ')' to 1L,
        ']' to 2L,
        '}' to 3L,
        '>' to 4L,
    )

    val matching = mapOf(
        ')' to '(',
        ']' to '[',
        '}' to '{',
        '>' to '<',
    )
    val reversed by lazy { matching.entries.associateBy({ it.value }) { it.key } }

    fun solve(inputs: List<String>): Long {
        val scores  = inputs
            .map { solver(it.toList()) }
            .filter { it.first == null && it.second.isNotEmpty() }
            .map { complete(it.second) }
            .map { score(it) }
            .sorted()
        return scores[scores.size / 2]
    }

    private fun score(chars: List<Char>) = chars.map { mapScore[it] ?: 0 }.reduce{res, x -> res * 5 + x }

    private fun complete(stack: List<Char>) = stack.map { reversed[it] }.filterNotNull()

    private fun solver(chars: List<Char>): Pair<Char?, List<Char>> {
        val stack = ArrayDeque<Char>()
        for(c in chars) {
            if(c in matching.keys) {
                if(stack.isEmpty()) {
                    return Pair(c, listOf())
                }
                val first = stack.removeFirst()
                if(first != matching[c]) {
                    return Pair(c, stack)
                }
            } else {
                stack.addFirst(c)
            }
        }
        return Pair(null, stack)
    }
}

fun main(args: Array<String>) {
    val inputs = Files.readAllLines(Path.of(args[0]))
    val result: Long
    val timeMs = measureTimeMillis {
        result = Day10b.solve(inputs)
    }

    println(result)
    println("$timeMs ms")
}