Solution 2017-22 (Sporifica Virus)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/extensions/grids/Coordinates.kt

@@ -59,6 +59,13 @@ enum class Direction(val row: Int, val col: Int) {
         WEST -> SOUTH
     }
 
+    fun reverse() = when (this) {
+        NORTH -> SOUTH
+        EAST -> WEST
+        SOUTH -> NORTH
+        WEST -> EAST
+    }
+
     fun asChar() = when (this) {
         NORTH -> '↑'
         EAST -> '→'

src/main/kotlin/de/ronny_h/aoc/year2017/day22/SporificaVirus.kt

@@ -0,0 +1,81 @@
+package de.ronny_h.aoc.year2017.day22
+
+import de.ronny_h.aoc.AdventOfCode
+import de.ronny_h.aoc.extensions.grids.Coordinates
+import de.ronny_h.aoc.extensions.grids.Direction.NORTH
+
+fun main() = SporificaVirus().run(5538, 2511090)
+
+class SporificaVirus : AdventOfCode<Int>(2017, 22) {
+    override fun part1(input: List<String>): Int {
+        val grid = SeeminglyInfiniteGrid(input)
+        grid.burst1(10000)
+        return grid.causedInfection
+    }
+
+    override fun part2(input: List<String>): Int {
+        val grid = SeeminglyInfiniteGrid(input)
+        grid.burst2(10000000)
+        return grid.causedInfection
+    }
+}
+
+class SeeminglyInfiniteGrid(input: List<String>) {
+    private val clean = '.'
+    private val infected = '#'
+    private val weakened = 'W'
+    private val flagged = 'F'
+
+    private val grid = mutableMapOf<Coordinates, Char>().withDefault { clean }
+
+    init {
+        input.forEachIndexed { row, line ->
+            line.forEachIndexed { col, node ->
+                grid[Coordinates(row, col)] = node
+            }
+        }
+    }
+
+    private var direction = NORTH
+    private var position = Coordinates(input.size / 2, input[0].length / 2)
+    var causedInfection = 0
+        private set
+
+    fun burst1(times: Int) = repeat(times) {
+        if (grid[position] == infected) {
+            direction = direction.turnRight()
+            grid[position] = clean
+        } else {
+            direction = direction.turnLeft()
+            grid[position] = infected
+            causedInfection++
+        }
+        position += direction
+    }
+
+    fun burst2(times: Int) = repeat(times) {
+        when (grid.getValue(position)) {
+            clean -> {
+                direction = direction.turnLeft()
+                grid[position] = weakened
+            }
+
+            weakened -> {
+                // no turn
+                grid[position] = infected
+                causedInfection++
+            }
+
+            infected -> {
+                direction = direction.turnRight()
+                grid[position] = flagged
+            }
+
+            flagged -> {
+                direction = direction.reverse()
+                grid[position] = clean
+            }
+        }
+        position += direction
+    }
+}

src/test/kotlin/de/ronny_h/aoc/extensions/grids/CoordinatesTest.kt

@@ -100,6 +100,13 @@ class CoordinatesTest : StringSpec({
         Direction.WEST.turnLeft() shouldBe Direction.SOUTH
     }
 
+    "Direction reverse() does a u-turn" {
+        Direction.NORTH.reverse() shouldBe Direction.SOUTH
+        Direction.EAST.reverse() shouldBe Direction.WEST
+        Direction.SOUTH.reverse() shouldBe Direction.NORTH
+        Direction.WEST.reverse() shouldBe Direction.EAST
+    }
+
     "asChar gives a graphical representation" {
         Direction.NORTH.asChar() shouldBe '↑'
         Direction.EAST.asChar() shouldBe '→'

src/test/kotlin/de/ronny_h/aoc/year2017/day22/SporificaVirusTest.kt

@@ -0,0 +1,22 @@
+package de.ronny_h.aoc.year2017.day22
+
+import de.ronny_h.aoc.extensions.asList
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class SporificaVirusTest : StringSpec({
+
+    val input = """
+            ..#
+            #..
+            ...
+        """.asList()
+
+    "part 1: The example causes 5587 infections in 10000 bursts" {
+        SporificaVirus().part1(input) shouldBe 5587
+    }
+
+    "part 2: The example causes 2511944 infections in 10000000 bursts" {
+        SporificaVirus().part2(input) shouldBe 2511944
+    }
+})