Advent of Code 2023 Day 3

day3.kt

import java.awt.Point
import java.io.File

fun main() {
    data class Digit(val p: Point, val value: Char)

    // List of digits is a number (always in right order because of parsing order)
    fun List<Digit>.value(): Long = this.map { it.value }.joinToString("").toLong()

    val matrix = File("input/day3.txt").readLines()
    val width = matrix[0].length
    val height = matrix.size

    // All points in the matrix
    val allPoints = (0..<height).flatMap { y ->
        (0..<width).map { x ->
            Point(x, y)
        }
    }

    // Get on character from the matrix, if out of bounds return '.'
    fun check(x: Int, y: Int): Char {
        return if (x < 0 || x >= width || y < 0 || y >= height) '.'
        else matrix[y][x]
    }

    // All points surrounding one point
    fun around(p: Point): List<Point> = (-1..1).map { x ->
        (-1..1).map { y -> Point(p.x + x, p.y + y) }
    }.flatten()

    // ALl points surrounding one number
    fun List<Digit>.around(): List<Point> = map { around(it.p) }.flatten()
    fun Char.isSymbol(): Boolean = !(this == '.' || this.isDigit())

    // Find all numbers and store
    var cNumber = mutableListOf<Digit>()
    val allNumbers = mutableListOf<List<Digit>>()
    allPoints.forEach { p ->
        if (matrix[p.y][p.x].isDigit()) {
            cNumber.add(Digit(Point(p.x, p.y), matrix[p.y][p.x]))
        } else {
            allNumbers.add(cNumber.toList())
            cNumber = mutableListOf()
        }
    }

    var sum = 0L
    allNumbers.forEach { nums ->
        if (nums.around().any { check(it.x, it.y).isSymbol() }) {
            sum += nums.value()
        }
    }
    println(sum)

    var bigSum = 0L
    allPoints.forEach { p ->
        if (matrix[p.y][p.x] == '*') {
            val matches = allNumbers.filter { nums ->
                nums.around().contains(p)
            }
            if (matches.size == 2) {
                val (a, b) = matches
                bigSum += a.value() * b.value()
            }
        }
    }
    println(bigSum)
}