Day01Trebuchet.kt

package adventofcode.year2023

import adventofcode.Puzzle
import adventofcode.PuzzleInput

class Day01Trebuchet(customInput: PuzzleInput? = null) : Puzzle(customInput) {
    override val name = "Trebuchet?!"

    override fun partOne() = input
        .lines()
        .sumOfFirstAndLastDigits()

    override fun partTwo() = input
        .lines()
        .map { line -> digitMap.entries.fold(line) { acc, (word, digit) -> acc.replace(word, "$word$digit$word") } }
        .sumOfFirstAndLastDigits()

    companion object {
        private val digitMap = mapOf(
            "one" to 1,
            "two" to 2,
            "three" to 3,
            "four" to 4,
            "five" to 5,
            "six" to 6,
            "seven" to 7,
            "eight" to 8,
            "nine" to 9
        )

        private fun List<String>.sumOfFirstAndLastDigits() = map { line -> line.filter(Char::isDigit) }
            .map { line -> String(charArrayOf(line.first(), line.last())) }
            .sumOf(String::toInt)
    }
}