AoC | Day 3 | Part 2

package year_2023.day_3

fun partTwo() {
    println("[2023] Day three, part two...")

    val input = input()

    val matrix = input.split("\n")
        .filter { it.isNotBlank() }
        .map { it.trim().split("") }
        .map { it.filter { it.isNotBlank() } }

    val specialCharacters = matrix.flatMap { it.map { it } }
        .filter { it.toIntOrNull() == null }
        .filter { it != "." }

    fun removeSpecialChars(row: String): String {
        var cleanRow = row
        specialCharacters.forEach {
            cleanRow = cleanRow.replace(it, ".")
        }
        return cleanRow
    }

    fun String.removeNumber(number: Int): String {
        return this.replaceFirst(
            number.toString(),
            (1..number.toString().length).joinToString("") { "." }
        )
    }


    val numberToDigitCoordinatesMapPt2 = input.split("\n").flatMapIndexed { idx, line ->
        var row = line.trim()
        val numbers = removeSpecialChars(row).split(".").mapNotNull { it.toIntOrNull() }
        numbers.map { number ->
            number to List(number.toString().length) { digitIdx ->
                CoordinatesPt2(row.indexOf("$number") + digitIdx, idx)
            }.also {
                row = row.removeNumber(number)
            }
        }
    }


    fun getGearCoordinates(coordinates: List<CoordinatesPt2>): Set<CoordinatesPt2> {
        return coordinates.flatMap {
            listOf(
                CoordinatesPt2(it.x - 1, it.y),
                CoordinatesPt2(it.x - 1, it.y - 1),
                CoordinatesPt2(it.x - 1, it.y + 1),

                CoordinatesPt2(it.x, it.y),
                CoordinatesPt2(it.x, it.y - 1),
                CoordinatesPt2(it.x, it.y + 1),

                CoordinatesPt2(it.x + 1, it.y),
                CoordinatesPt2(it.x + 1, it.y - 1),
                CoordinatesPt2(it.x + 1, it.y + 1),
            )
        }
            .filter { it.x >= 0 && it.y >= 0 }
            .filter { it.x < matrix.size && it.y < matrix[0].size }
            .filter { it !in coordinates }
            .filter { matrix[it.y][it.x] == "*" }
            .toSet()
    }

    val mapOfGears = mutableMapOf<CoordinatesPt2, MutableList<Int>>()
    numberToDigitCoordinatesMapPt2.forEach { (number, coordinates) ->
        val gearCoordinate = getGearCoordinates(coordinates)
        gearCoordinate.forEach {
            if (mapOfGears[it] == null) {
                mapOfGears[it] = mutableListOf()
            }

            mapOfGears[it]!!.add(number)
        }
    }

    val sumOfRatios = mapOfGears.filter { it.value.size == 2 }.values.sumOf { it[0] * it[1] }
    println(sumOfRatios)
}

private data class CoordinatesPt2(val x: Int, val y: Int)