Add solution for Y2024D09.

Author: Jadarma

Diff for: README.md

@@ -15,17 +15,18 @@ _"Anything that's worth doing, is worth overdoing."_
 Table of contents to jump straight to the problem you're looking for.
 
 <details open>
-    <summary>2024 (14x⭐)</summary>
-
-| Day | Title                                                   | Stars |
-|:---:|:--------------------------------------------------------|:-----:|
-| 01  | [Historian Hysteria](solutions/aockt/y2024/Y2024D01.kt) |  ⭐⭐   |
-| 02  | [Red-Nosed Reports](solutions/aockt/y2024/Y2024D02.kt)  |  ⭐⭐   |
-| 03  | [Mull It Over](solutions/aockt/y2024/Y2024D03.kt)       |  ⭐⭐   |
-| 04  | [Ceres Search](solutions/aockt/y2024/Y2024D04.kt)       |  ⭐⭐   |
-| 05  | [Print Queue](solutions/aockt/y2024/Y2024D05.kt)        |  ⭐⭐   |
-| 06  | [Guard Gallivant](solutions/aockt/y2024/Y2024D06.kt)    |  ⭐⭐   |
-| 07  | [Bridge Repair](solutions/aockt/y2024/Y2024D07.kt)      |  ⭐⭐   |
+    <summary>2024 (16x⭐)</summary>
+
+| Day | Title                                                      | Stars |
+|:---:|:-----------------------------------------------------------|:-----:|
+| 01  | [Historian Hysteria](solutions/aockt/y2024/Y2024D01.kt)    |  ⭐⭐   |
+| 02  | [Red-Nosed Reports](solutions/aockt/y2024/Y2024D02.kt)     |  ⭐⭐   |
+| 03  | [Mull It Over](solutions/aockt/y2024/Y2024D03.kt)          |  ⭐⭐   |
+| 04  | [Ceres Search](solutions/aockt/y2024/Y2024D04.kt)          |  ⭐⭐   |
+| 05  | [Print Queue](solutions/aockt/y2024/Y2024D05.kt)           |  ⭐⭐   |
+| 06  | [Guard Gallivant](solutions/aockt/y2024/Y2024D06.kt)       |  ⭐⭐   |
+| 07  | [Bridge Repair](solutions/aockt/y2024/Y2024D07.kt)         |  ⭐⭐   |
+| 08  | [Resonant Collinearity](solutions/aockt/y2024/Y2024D08.kt) |  ⭐⭐   |
 
 </details>
 

Diff for: inputs/aockt/y2024/d08/input.txt

@@ -0,0 +1,55 @@
+package aockt.y2024
+
+import aockt.util.math.distinctPairs
+import aockt.util.parse
+import aockt.util.spacial.*
+import io.github.jadarma.aockt.core.Solution
+
+object Y2024D08 : Solution {
+
+    /**
+     * The map of antennas on the Easter Bunny roof.
+     * @property area The bounds to check nodes in.
+     * @property antennas All the antenna positions, group by the frequencies they emit.
+     */
+    private class AntennaMap(val area: Area, val antennas: Map<Char, Set<Point>>) {
+
+        /**
+         * Return all the unique points within the [area] that form at least one frequency anti-node.
+         * If [repeating] is enabled, an anti-node will spawn at every collinear interval between two matching
+         * antennas _(including themselves)_.
+         */
+        fun antiNodes(repeating: Boolean = false): Set<Point> = buildSet {
+            antennas.values
+                .asSequence()
+                .flatMap(Set<Point>::distinctPairs)
+                .forEach { (a, b) ->
+                    val dx = a.x - b.x
+                    val dy = a.y - b.y
+                    var step = if (repeating) 0 else 1
+                    while (repeating || step == 1) {
+                        val p1 = Point(x = a.x + dx * step, y = a.y + dy * step).takeIf { it in area }?.let(::add)
+                        val p2 = Point(x = b.x - dx * step, y = b.y - dy * step).takeIf { it in area }?.let(::add)
+                        if (p1 == null && p2 == null) break
+                        step++
+                    }
+                }
+        }
+    }
+
+    /** Parse the [input] and return the [AntennaMap]. */
+    private fun parseInput(input: String): AntennaMap = parse {
+        with(Grid(input)) {
+            AntennaMap(
+                area = Area(width, height),
+                antennas = points()
+                    .filter { it.value != '.' }
+                    .groupBy({ it.value }, { it.position })
+                    .mapValues { (_, points) -> points.toSet() },
+            )
+        }
+    }
+
+    override fun partOne(input: String): Int = parseInput(input).antiNodes(repeating = false).count()
+    override fun partTwo(input: String): Int = parseInput(input).antiNodes(repeating = true).count()
+}

Diff for: inputs/aockt/y2024/d08/solution_part1.txt

@@ -0,0 +1,45 @@
+package aockt.y2024
+
+import io.github.jadarma.aockt.test.AdventDay
+import io.github.jadarma.aockt.test.AdventSpec
+
+@AdventDay(2024, 8, "Resonant Collinearity")
+class Y2024D08Test : AdventSpec<Y2024D08>({
+
+    val exampleInput = """
+        ............
+        ........0...
+        .....0......
+        .......0....
+        ....0.......
+        ......A.....
+        ............
+        ............
+        ........A...
+        .........A..
+        ............
+        ............
+    """.trimIndent()
+
+    val exampleT = """
+        T.........
+        ...T......
+        .T........
+        ..........
+        ..........
+        ..........
+        ..........
+        ..........
+        ..........
+        ..........
+    """.trimIndent()
+
+    partOne {
+        exampleInput shouldOutput 14
+    }
+
+    partTwo {
+        exampleInput shouldOutput 34
+        exampleT shouldOutput 9
+    }
+})