Solution 2017-19 (Particle Swarm)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year2017/day19/ParticleSwarm.kt

@@ -0,0 +1,55 @@
+package de.ronny_h.aoc.year2017.day19
+
+import de.ronny_h.aoc.AdventOfCode
+import de.ronny_h.aoc.extensions.grids.Coordinates
+import de.ronny_h.aoc.extensions.grids.Direction
+import de.ronny_h.aoc.extensions.grids.Direction.*
+import de.ronny_h.aoc.extensions.grids.SimpleCharGrid
+
+fun main() = ParticleSwarm().run("EOCZQMURF", "16312")
+
+class ParticleSwarm : AdventOfCode<String>(2017, 19) {
+    override fun part1(input: List<String>): String = RoutingDiagram(input).followThePath().letters
+
+    override fun part2(input: List<String>): String = RoutingDiagram(input).followThePath().length.toString()
+}
+
+data class Path(val letters: String, val length: Int)
+
+class RoutingDiagram(input: List<String>) : SimpleCharGrid(input, ' ') {
+    fun findStartCoordinates(): Coordinates = find('|')
+
+    fun followThePath(): Path {
+        val letters = mutableListOf<Char>()
+        var position = findStartCoordinates()
+        var direction = SOUTH
+        var steps = 0
+
+        while (getAt(position) != nullElement) {
+            if (getAt(position).isLetter()) {
+                letters.add(getAt(position))
+            }
+
+            position += direction
+            steps++
+
+            if (getAt(position) == '+') {
+                val turnRight = direction.turnRight()
+                val charAtRight = getAt(position + turnRight)
+                direction = if (charAtRight == turnRight.char() || charAtRight.isLetter()) {
+                    turnRight
+                } else {
+                    direction.turnLeft()
+                }
+            }
+        }
+        return Path(letters.joinToString(""), steps)
+    }
+
+    private fun Direction.char() = when (this) {
+        NORTH -> '|'
+        EAST -> '-'
+        SOUTH -> '|'
+        WEST -> '-'
+    }
+}

src/test/kotlin/de/ronny_h/aoc/year2017/day19/ParticleSwarmTest.kt

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+package de.ronny_h.aoc.year2017.day19
+
+import de.ronny_h.aoc.extensions.asList
+import de.ronny_h.aoc.extensions.grids.Coordinates
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class ParticleSwarmTest : StringSpec({
+
+    val input = """
+        #     |          
+        #     |  +--+    
+        #     A  |  C    
+        # F---|----E|--+ 
+        #     |  |  |  D 
+        #     +B-+  +--+ 
+    """.trimMargin("#").asList()
+
+    "input can be parsed" {
+        RoutingDiagram(input).findStartCoordinates() shouldBe Coordinates(0, 4)
+    }
+
+    "part 1: the letters on the path from the beginning to the end" {
+        ParticleSwarm().part1(input) shouldBe "ABCDEF"
+    }
+
+    "part 2: the package takes a total of 38 steps" {
+        ParticleSwarm().part2(input) shouldBe "38"
+    }
+})