Solution 2018-13, part 1 (Mine Cart Madness)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year2018/day13/MineCartMadness.kt

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+package de.ronny_h.aoc.year2018.day13
+
+import de.ronny_h.aoc.AdventOfCode
+import de.ronny_h.aoc.extensions.collections.firstDuplicate
+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
+import de.ronny_h.aoc.extensions.grids.Turn
+import de.ronny_h.aoc.extensions.grids.Turn.*
+
+fun main() = MineCartMadness().run("33,69", "")
+
+class MineCartMadness : AdventOfCode<String>(2018, 13) {
+    override fun part1(input: List<String>): String {
+        val collision = Track(input).moveCartsUntilFirstCrash()
+        return "${collision.col},${collision.row}"
+    }
+
+    override fun part2(input: List<String>): String {
+        return ""
+    }
+}
+
+class Track(input: List<String>) : SimpleCharGrid(input, ' ') {
+    private val carts: List<Cart> = buildList {
+        forEachCoordinates { position, element ->
+            when (element) {
+                '<' -> {
+                    add(Cart(position, WEST))
+                    setAt(position, '-')
+                }
+
+                '>' -> {
+                    add(Cart(position, EAST))
+                    setAt(position, '-')
+                }
+
+                '^' -> {
+                    add(Cart(position, NORTH))
+                    setAt(position, '|')
+                }
+
+                'v' -> {
+                    add(Cart(position, SOUTH))
+                    setAt(position, '|')
+                }
+            }
+        }.last()
+    }
+
+    fun moveCartsUntilFirstCrash(): Coordinates {
+        var collision: Coordinates? = null
+        while (collision == null) {
+            collision = tick()
+        }
+        return collision
+    }
+
+    private fun tick(): Coordinates? {
+        for (cart in carts.sortedBy { it.position }) {
+            cart.move()
+            carts.firstDuplicate(Cart::position)?.also { return it }
+        }
+        return null
+    }
+
+    private fun Cart.move() {
+        position += direction
+        direction = when (getAt(position)) {
+            '+' -> direction.turn(nextTurn())
+            '/' -> if (direction == NORTH || direction == SOUTH) direction.turnRight() else direction.turnLeft()
+            '\\' -> if (direction == NORTH || direction == SOUTH) direction.turnLeft() else direction.turnRight()
+            else -> direction
+        }
+    }
+}
+
+data class Cart(var position: Coordinates, var direction: Direction, private var lastTurn: Turn = RIGHT) {
+    fun nextTurn(): Turn {
+        lastTurn = when (lastTurn) {
+            LEFT -> STRAIGHT
+            STRAIGHT -> RIGHT
+            RIGHT -> LEFT
+        }
+        return lastTurn
+    }
+}

src/test/kotlin/de/ronny_h/aoc/year2018/day13/MineCartMadnessTest.kt

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+package de.ronny_h.aoc.year2018.day13
+
+import de.ronny_h.aoc.extensions.asList
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class MineCartMadnessTest : StringSpec({
+
+    val input = """
+        /->-\        
+        |   |  /----\
+        | /-+--+-\  |
+        | | |  | v  |
+        \-+-/  \-+--/
+          \------/   
+    """.asList()
+
+    "part 1: the location of the first crash" {
+        MineCartMadness().part1(input) shouldBe "7,3"
+    }
+
+    "part 2" {
+        val input = listOf("")
+        MineCartMadness().part2(input) shouldBe ""
+    }
+})