aoc_2024/day04.kts

#!/usr/bin/env kotlin
import java.io.File
import java.util.Scanner

val scanner = Scanner(System.`in`)
val xMasSearchWord = listOf("M", "A", "S") // Skip X because that triggers the search at 0,0 offset.
val xMasSearchOffsets = listOf(
    listOf(Pair(0, 1), Pair(0, 2), Pair(0, 3)),
    listOf(Pair(1, 0), Pair(2, 0), Pair(3, 0)),
    listOf(Pair(0, -1), Pair(0, -2), Pair(0, -3)),
    listOf(Pair(-1, 0), Pair(-2, 0), Pair(-3, 0)),
    listOf(Pair(1, 1), Pair(2, 2), Pair(3, 3)),
    listOf(Pair(-1, 1), Pair(-2, 2), Pair(-3, 3)),
    listOf(Pair(-1, -1), Pair(-2, -2), Pair(-3, -3)),
    listOf(Pair(1, -1), Pair(2, -2), Pair(3, -3))
)
var ycoordinates = mutableListOf<List<String>>()
while (scanner.hasNextLine()) {
    val line = scanner.nextLine()
    val xcoordinates = line.split("").filter { it.isNotEmpty() }
    ycoordinates.add(xcoordinates)
}
var xMasCount = 0
var masXCount = 0
for (y in ycoordinates.indices) {
    for (x in ycoordinates[y].indices) {
        if (ycoordinates[y][x] == "X") {
            xMasCount += findXmas(y, x)
        }
        if (ycoordinates[y][x] == "A") {
            masXCount += findMasX(y, x)
        }
    }
}

fun findXmas(y: Int, x: Int): Int {
    println("x: $x, y: $y")
    var xmasfound = 0
    for (searchOffset in xMasSearchOffsets) {
        val last = searchOffset.last()
        if ((y+last.first) !in ycoordinates.indices || (x+last.second) !in ycoordinates[y].indices){
            if (x == 1 && y == 139) println("skipping x: (${x+last.second}, y: ${y+last.first})")
            continue
        }
        var match = true
        for (i in searchOffset.indices) {
            val (dy, dx) = searchOffset[i]
            val search = xMasSearchWord[i]
            if (ycoordinates[y+dy][x+dx] != search) {
                match = false
                break
            }
        }
        if (match) {
            xmasfound += 1
        }
    }
    return xmasfound
}

println("Xmas count: $xMasCount")
println("Mas X count: $masXCount")

fun findMasX(y: Int, x: Int): Int {
    if (y == 0 || x == 0 || y == ycoordinates.lastIndex || x == ycoordinates[y].lastIndex) {
        return 0
    }
    val validChars = mutableListOf("M", "S")
    if (ycoordinates[y - 1][x - 1] !in validChars) {
        return 0
    }
    val remainsOne = validChars[if(validChars.indexOf(ycoordinates[y - 1][x - 1]) == 0) 1 else 0]
    if (ycoordinates[y + 1][x + 1] != remainsOne) {
        return 0
    }
    if (ycoordinates[y - 1][x + 1] !in validChars) {
        return 0
    }
    val remainsTwo = validChars[if(validChars.indexOf(ycoordinates[y - 1][x + 1]) == 0) 1 else 0]
    if (ycoordinates[y + 1][x - 1] != remainsTwo) {
        return 0
    }
    return 1
}