Solution 2016-01 (No Time for a Taxicab)

Author: rhaendel

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

@@ -3,6 +3,10 @@ package de.ronny_h.aoc.extensions
 import kotlin.math.abs
 
 data class Coordinates(val row: Int, val col: Int) {
+
+    companion object {
+        val ZERO = Coordinates(0, 0)
+    }
     operator fun plus(other: Coordinates) = Coordinates(row + other.row, col + other.col)
     operator fun minus(other: Coordinates) = Coordinates(row - other.row, col - other.col)
 

src/main/kotlin/de/ronny_h/aoc/year2016/day01/NoTimeForATaxicab.kt

@@ -0,0 +1,44 @@
+package de.ronny_h.aoc.year2016.day01
+
+import de.ronny_h.aoc.AdventOfCode
+import de.ronny_h.aoc.extensions.Coordinates
+import de.ronny_h.aoc.extensions.Coordinates.Companion.ZERO
+import de.ronny_h.aoc.extensions.Direction.NORTH
+
+fun main() = NoTimeForATaxicab().run(239, 141)
+
+class NoTimeForATaxicab : AdventOfCode<Int>(2016, 1) {
+    override fun part1(input: List<String>): Int = input.parseInstructions().followInstructions() taxiDistanceTo ZERO
+
+    private fun List<String>.parseInstructions(): List<String> = first().split(", ")
+
+    private fun List<String>.followInstructions(stopAtFirstLocationVisitedTwice: Boolean = false): Coordinates {
+        var position = ZERO
+        var direction = NORTH
+        val visited = mutableSetOf(position)
+
+        forEach {
+            val turn = it.first()
+            val steps = it.substring(1).toInt()
+
+            direction = when (turn) {
+                'L' -> direction.turnLeft()
+                'R' -> direction.turnRight()
+                else -> error("Invalid turn: $turn")
+            }
+
+            repeat(steps) {
+                position += direction
+                if (stopAtFirstLocationVisitedTwice) {
+                    if (!visited.add(position)) {
+                        return position
+                    }
+                }
+            }
+        }
+        return position
+    }
+
+    override fun part2(input: List<String>): Int =
+        input.parseInstructions().followInstructions(true) taxiDistanceTo ZERO
+}

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

@@ -42,6 +42,10 @@ class CoordinatesTest : StringSpec({
         }
     }
 
+    "Coordinates of ZERO" {
+        Coordinates.ZERO shouldBe Coordinates(0, 0)
+    }
+
     "Add a direction" {
         forAll(
             row(Coordinates(5, 5), NORTH, Coordinates(4, 5)),

src/test/kotlin/de/ronny_h/aoc/year2016/day01/NoTimeForATaxicabTest.kt

@@ -0,0 +1,27 @@
+package de.ronny_h.aoc.year2016.day01
+
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class NoTimeForATaxicabTest : StringSpec({
+
+    "part 1, small example" {
+        NoTimeForATaxicab().part1(listOf("R2, L3")) shouldBe 5
+    }
+
+    "part 1, medium example" {
+        NoTimeForATaxicab().part1(listOf("R2, R2, R2")) shouldBe 2
+    }
+
+    "part 1, large example" {
+        NoTimeForATaxicab().part1(listOf("R5, L5, R5, R3")) shouldBe 12
+    }
+
+    "part 1, negative x, positive y coordinate" {
+        NoTimeForATaxicab().part1(listOf("L1, R1")) shouldBe 2
+    }
+
+    "part 2: the first location visited twice" {
+        NoTimeForATaxicab().part2(listOf("R8, R4, R4, R8")) shouldBe 4
+    }
+})