Day 14

Author: WVerlaek

src/main/kotlin/y24/Day14.kt

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+package y24
+
+import common.puzzle.solvePuzzle
+import common.puzzle.Input
+import common.puzzle.Puzzle
+import common.datastructures.*
+import common.ext.*
+import common.util.*
+import java.util.*
+import kotlin.math.*
+import kotlin.system.exitProcess
+
+
+fun main() = solvePuzzle(year = 2024, day = 14, dryRun = true) { Day14(it) }
+
+class Day14(val input: Input, val rows: Int = 103, val cols: Int = 101) : Puzzle {
+
+    data class Robot(val p: Point, val v: Point)
+
+    private fun Robot.move(n: Int): Robot {
+        var x = p.x + v.x * n
+        while (x < 0) x += cols
+        var y = p.y + v.y * n
+        while (y < 0) y += rows
+
+        return Robot(Point(
+            col = x % cols,
+            row = y % rows,
+        ), v)
+    }
+
+    private val robots = input.lines.map { line ->
+        val p = Point.parse(line.substringBetween("p=", " "))
+        val v = Point.parse(line.substringAfter("v="))
+        Robot(p, v)
+    }
+
+    override fun solveLevel1(): Any {
+        val moved = robots.map { it.move(100) }
+        val quadrants = moved.groupBy { robot ->
+            val qx = robot.p.x.compareTo(cols / 2).sign
+            val qy = robot.p.y.compareTo(rows / 2).sign
+            qx to qy
+        }.filterKeys { (qx, qy) -> qx != 0 && qy != 0 }
+
+        return quadrants.values.fold(1) { acc, robots -> acc * robots.size }
+    }
+
+    override fun solveLevel2(): Any {
+        var robots = robots
+        repeat(10000) { i ->
+            val grid = Grid(rows, cols) { _, _ -> false }
+            var numInEdge = 0
+            robots.forEach { r ->
+                grid[r.p].value = true
+                if (r.p.x !in (5..cols-5)) {
+                    numInEdge++
+                }
+            }
+            if (numInEdge < 20) {
+                // Tree will be mostly in the center, so only print the ones that don't have many
+                // robots on the left/right sides.
+                println("$i:")
+                println(grid)
+                println()
+            }
+            robots = robots.map { it.move(1) }
+        }
+
+        return -1
+    }
+}

src/test/kotlin/y24/Day14Test.kt

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+package y24
+
+import common.puzzle.Input
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+
+internal class Day14Test {
+    private val sample = Input("""
+    p=0,4 v=3,-3
+    p=6,3 v=-1,-3
+    p=10,3 v=-1,2
+    p=2,0 v=2,-1
+    p=0,0 v=1,3
+    p=3,0 v=-2,-2
+    p=7,6 v=-1,-3
+    p=3,0 v=-1,-2
+    p=9,3 v=2,3
+    p=7,3 v=-1,2
+    p=2,4 v=2,-3
+    p=9,5 v=-3,-3
+    """.trimIndent())
+
+    private val day = Day14(sample, rows = 7, cols = 11)
+
+    @Test
+    fun solveLevel1() {
+        assertEquals(12, day.solveLevel1())
+    }
+
+    @Test
+    fun solveLevel2() {
+        // Manual solution
+    }
+}