Solution 2015-14 (Reindeer Olympics)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year2015/day14/ReindeerOlympics.kt

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+package de.ronny_h.aoc.year2015.day14
+
+import de.ronny_h.aoc.AdventOfCode
+import kotlin.math.min
+
+fun main() = ReindeerOlympics().run(2660, 1256)
+
+class ReindeerOlympics : AdventOfCode<Int>(2015, 14) {
+    override fun part1(input: List<String>): Int = input.parse().maxReindeerDistanceIn(2503)
+    override fun part2(input: List<String>): Int = input.parse().pointsOfWinnerIn(2503)
+}
+
+fun List<Reindeer>.maxReindeerDistanceIn(secondsTotal: Int) = map { it.reindeerDistanceIn(secondsTotal) }.max()
+
+fun List<Reindeer>.pointsOfWinnerIn(secondsTotal: Int): Int {
+    val reindeerPoints = MutableList(size) { 0 }
+    for (seconds in 1..secondsTotal) {
+        val distances = map { it.reindeerDistanceIn(seconds) }.withIndex()
+        val leaderDistance = distances.maxOf { it.value }
+        val leaders = distances.filter { it.value == leaderDistance }
+        leaders.forEach {
+            reindeerPoints[it.index]++
+        }
+    }
+    return reindeerPoints.max()
+}
+
+private fun Reindeer.reindeerDistanceIn(secondsTotal: Int): Int {
+    val cycleDuration = flyDuration + restDuration
+    val cycles = secondsTotal / cycleDuration
+    val remainingFlyDuration = min(secondsTotal - (cycleDuration * cycles), flyDuration)
+    return speed * (flyDuration * cycles + remainingFlyDuration)
+}
+
+data class Reindeer(val speed: Int, val flyDuration: Int, val restDuration: Int)
+
+fun List<String>.parse() = map {
+    val (speed, flyDuration, restDuration) = it
+        .substringAfter(" can fly ")
+        .substringBeforeLast(" seconds.")
+        .split(" km/s for ", " seconds, but then must rest for ")
+    Reindeer(speed.toInt(), flyDuration.toInt(), restDuration.toInt())
+}

src/test/kotlin/de/ronny_h/aoc/year2015/day14/ReindeerOlympicsTest.kt

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+package de.ronny_h.aoc.year2015.day14
+
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class ReindeerOlympicsTest : StringSpec({
+
+    val input = listOf(
+        "Comet can fly 14 km/s for 10 seconds, but then must rest for 127 seconds.",
+        "Dancer can fly 16 km/s for 11 seconds, but then must rest for 162 seconds.",
+    )
+    val parsedInput = listOf(
+        Reindeer(14, 10, 127),
+        Reindeer(16, 11, 162),
+    )
+
+    "input can be parsed" {
+        input.parse() shouldBe parsedInput
+    }
+
+    "part 1: max Reindeer distance in 1000 seconds" {
+        parsedInput.maxReindeerDistanceIn(1000) shouldBe 1120
+    }
+
+    "part 2: points of the winner in 1000 seconds" {
+        parsedInput.pointsOfWinnerIn(1000) shouldBe 689
+    }
+})