AoC | Day 3 | Part 1

package year_2023.day_3

fun partOne() {
    println("[2023] Day three, part one...")

    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 numberToDigitCoordinatesMap = 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 ->
                Coordinates(row.indexOf("$number") + digitIdx, idx)
            }.also {
                row = row.removeNumber(number)
            }
        }
    }


    fun numberIsPartNumber(coordinates: List<Coordinates>): Boolean {
        val coordinatesAround = coordinates.flatMap {
            listOf(
                Coordinates(it.x - 1, it.y),
                Coordinates(it.x - 1, it.y - 1),
                Coordinates(it.x - 1, it.y + 1),

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

                Coordinates(it.x + 1, it.y),
                Coordinates(it.x + 1, it.y - 1),
                Coordinates(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 }
            .toSet()

        return coordinatesAround.any {
            val point = matrix[it.y][it.x]
            point.toIntOrNull() == null && point != "."
        }
    }

    var sumOfPartNumbers = 0
    numberToDigitCoordinatesMap.forEach { (number, coordinates) ->
        if (numberIsPartNumber(coordinates)) {
            sumOfPartNumbers += number
        }
    }

    println(sumOfPartNumbers)
}

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