Solution 2015-03 (Perfectly Spherical Houses in a Vacuum)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year2015/day03/PerfectlySphericalHouses.kt

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+package de.ronny_h.aoc.year2015.day03
+
+import de.ronny_h.aoc.AdventOfCode
+import de.ronny_h.aoc.extensions.Coordinates
+import de.ronny_h.aoc.extensions.Direction
+
+fun main() = PerfectlySphericalHouses().run(2592, 2360)
+
+class PerfectlySphericalHouses : AdventOfCode<Int>(2015, 3) {
+    override fun part1(input: List<String>): Int {
+        require(input.size == 1)
+        var position = Coordinates(0, 0)
+        val visited = mutableSetOf<Coordinates>(position)
+        input.parseDirections()
+            .forEach {
+                position += it
+                visited.add(position)
+            }
+        return visited.size
+    }
+
+    override fun part2(input: List<String>): Int {
+        require(input.size == 1)
+        var santaPosition = Coordinates(0, 0)
+        var robotSantaPosition = santaPosition
+        val visited = mutableSetOf<Coordinates>(santaPosition)
+        input.parseDirections()
+            .forEachIndexed { i, direction ->
+                if (i % 2 == 0) {
+                    robotSantaPosition += direction
+                    visited.add(robotSantaPosition)
+                } else {
+                    santaPosition += direction
+                    visited.add(santaPosition)
+                }
+            }
+        return visited.size
+    }
+
+    private fun List<String>.parseDirections() = first()
+        .map {
+            when (it) {
+                '^' -> Direction.NORTH
+                'v' -> Direction.SOUTH
+                '>' -> Direction.EAST
+                '<' -> Direction.WEST
+                else -> error("invalid direction: $it")
+            }
+        }
+}

src/test/kotlin/de/ronny_h/aoc/year2015/day03/PerfectlySphericalHousesTest.kt

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+package de.ronny_h.aoc.year2015.day03
+
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class PerfectlySphericalHousesTest : StringSpec({
+
+    "part 1: Santa delivers at least one present to a number of houses" {
+        PerfectlySphericalHouses().part1(listOf(">")) shouldBe 2
+        PerfectlySphericalHouses().part1(listOf("^>v<")) shouldBe 4
+        PerfectlySphericalHouses().part1(listOf("^v^v^v^v^v")) shouldBe 2
+    }
+
+    "part 2: Santa and Robo-Santa deliver at least one present to a number of houses" {
+        PerfectlySphericalHouses().part2(listOf("^v")) shouldBe 3
+        PerfectlySphericalHouses().part2(listOf("^>v<")) shouldBe 3
+        PerfectlySphericalHouses().part2(listOf("^v^v^v^v^v")) shouldBe 11
+    }
+})