2024 Day 08

Author: fibsifan

src/main/kotlin/de/jball/aoc2024/day08/Day08.kt

@@ -0,0 +1,60 @@
+package de.jball.aoc2024.day08
+
+import de.jball.AdventOfCodeDay
+import de.jball.aocutils.Grid
+import de.jball.aocutils.Point
+import kotlin.math.sin
+
+class Day08(test: Boolean = false): AdventOfCodeDay<Int>(test, 14, 34) {
+
+	val antennas = Grid.parse(input, '.')
+
+	override fun part1(): Int {
+
+		val antennaLocationsByType = antennas.map.entries
+			.groupBy({ it.value }, { it.key })
+
+		val candidates = antennaLocationsByType.entries.flatMap { antiNodes(it.value) }
+		return candidates.toSet().size
+	}
+
+	private fun antiNodes(input: List<Point>, fullLines: Boolean = false): Set<Point> {
+		if (input.size < 2) return setOf()
+
+		val candidates = (0 until input.size).flatMap { i ->
+			((i + 1) until input.size).flatMap { j ->
+				antiNodes(input[i], input[j], fullLines)
+			}
+		}
+
+		return candidates.toSet()
+	}
+
+	private fun antiNodes(a: Point, b: Point, line: Boolean = false): List<Point> {
+		val delta = a-b
+		val positives = generateSequence(a) { it + delta }
+			.let { if (line) it else it.drop(1) }
+			.takeWhile { this.antennas.isPointInGrid(it) }
+			.let { if (line) it else it.take(1) }
+			.toList()
+		val negatives = generateSequence(b) { it - delta }
+			.let { if (line) it else it.drop(1) }
+			.takeWhile { this.antennas.isPointInGrid(it) }
+			.let { if (line) it else it.take(1) }
+			.toList()
+
+		return positives + negatives
+	}
+
+	override fun part2(): Int {
+		val antennaLocationsByType = antennas.map.entries
+			.groupBy({ it.value }, { it.key })
+
+		val candidates = antennaLocationsByType.entries.flatMap { antiNodes(it.value, fullLines = true) }
+		return candidates.toSet().size
+	}
+}
+
+fun main() {
+	Day08().run()
+}

src/main/kotlin/de/jball/aocutils/Grid.kt

@@ -21,6 +21,11 @@ open class Grid<T>(val map: Map<Point, T>, val width: Int, val height: Int, priv
 		}
 	}
 
+	fun isPointInGrid(point: Point): Boolean {
+		val (x, y) = point
+		return (x in 0..<width && y in 0..<height)
+	}
+
 	override fun toString(): String {
 		return (height-1 downTo 0).map { row ->
 			(0 ..< width).map { column ->

src/test/kotlin/de/jball/aoc2024/Tests2024.kt

@@ -7,6 +7,7 @@ import de.jball.aoc2024.day04.Day04
 import de.jball.aoc2024.day05.Day05
 import de.jball.aoc2024.day06.Day06
 import de.jball.aoc2024.day07.Day07
+import de.jball.aoc2024.day08.Day08
 import kotlin.test.Test
 
 class Tests2024 {
@@ -44,4 +45,9 @@ class Tests2024 {
 	fun day07() {
 		Day07(true).run()
 	}
+
+	@Test
+	fun day08() {
+		Day08(true).run()
+	}
 }

src/test/resources/2024/Day08.txt

@@ -0,0 +1,12 @@
+............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............