118 lines
4.4 KiB
Kotlin
118 lines
4.4 KiB
Kotlin
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import java.io.File
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typealias Coordinate = Pair<Int, Int>
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fun main() {
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val input = File("input")
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var numbers: MutableMap<Coordinate, Int> = mutableMapOf()
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var symbols: MutableMap<Coordinate, Char> = mutableMapOf()
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input.useLines {
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it.forEachIndexed { row, line ->
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line.forEachIndexed { col, char ->
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when (char) {
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in '0'..'9' -> {
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// In this case, we're either starting a new
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// number, or in the middle of an existing
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// number.
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// We need to mark all previous coordinates as
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// well as this one as the full multi-digit
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// number, so we need to check the previous
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// columns.
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var length = 1
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while (numbers.get(Coordinate(row, col - length)) != null) {
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length += 1
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}
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// Now we check if the column already has a
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// number; if not, we're starting a new one,
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// otherwise mark this column as well as any
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// previous ones as the new number.
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val number = numbers.get(Coordinate(row, col - length + 1))
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if (number == null) {
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numbers.put(Coordinate(row, col), char.digitToInt())
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} else {
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for (coordinate in col downTo col - length + 1) {
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numbers.put(
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Coordinate(row, coordinate),
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number * 10 + char.digitToInt()
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)
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}
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}
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}
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// Dots are ignored
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'.' -> Unit
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// Collect the coordinates of all symbols, too
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else -> symbols.put(Coordinate(row, col), char)
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}
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}
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}
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}
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val gears: List<Int> =
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symbols
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.map { symbol ->
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if (symbol.value == '*') {
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var adjacent = 0
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var last: Int? = null
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var ratio = 1
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for (coord in nextTo(symbol.key)) {
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val number = numbers.get(coord)
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if (number != last && number != null) {
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last = number
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adjacent += 1
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ratio *= number
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}
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}
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if (adjacent == 2) {
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ratio
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} else {
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null
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}
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} else {
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null
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}
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}
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.filterNotNull()
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println("Part 1: ${gears.sum()}")
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val parts =
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symbols.flatMap { symbol ->
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nextTo(symbol.key)
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.map {
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val number = numbers.remove(it)
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if (number == null) {
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number
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} else {
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var prev: Coordinate = it
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do {
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prev = Coordinate(prev.first, prev.second - 1)
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} while (numbers.remove(prev) != null)
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var next: Coordinate = it
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do {
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next = Coordinate(next.first, next.second + 1)
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} while (numbers.remove(next) != null)
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number
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}
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}
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.filterNotNull()
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}
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println("Part 2: ${parts.sum()}")
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}
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fun nextTo(coordinate: Coordinate): List<Coordinate> {
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return (coordinate.first - 1..coordinate.first + 1).flatMap { row ->
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(coordinate.second - 1..coordinate.second + 1).map { col -> Coordinate(row, col) }
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}
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}
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