Add 2021 - Day 6 - Part 2

2021/06/input/1.txt

@@ -0,0 +1 @@
+1,3,4,1,1,1,1,1,1,1,1,2,2,1,4,2,4,1,1,1,1,1,5,4,1,1,2,1,1,1,1,4,1,1,1,4,4,1,1,1,1,1,1,1,2,4,1,3,1,1,2,1,2,1,1,4,1,1,1,4,3,1,3,1,5,1,1,3,4,1,1,1,3,1,1,1,1,1,1,1,1,1,1,1,1,1,5,2,5,5,3,2,1,5,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,5,1,1,1,1,5,1,1,1,1,1,4,1,1,1,1,1,3,1,1,1,1,1,1,1,1,1,1,1,3,1,2,4,1,5,5,1,1,5,3,4,4,4,1,1,1,2,1,1,1,1,1,1,2,1,1,1,1,1,1,5,3,1,4,1,1,2,2,1,2,2,5,1,1,1,2,1,1,1,1,3,4,5,1,2,1,1,1,1,1,5,2,1,1,1,1,1,1,5,1,1,1,1,1,1,1,5,1,4,1,5,1,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,5,4,5,1,1,1,1,1,1,1,5,1,1,3,1,1,1,3,1,4,2,1,5,1,3,5,5,2,1,3,1,1,1,1,1,3,1,3,1,1,2,4,3,1,4,2,2,1,1,1,1,1,1,1,5,2,1,1,1,2

2021/06/main.kt

@@ -0,0 +1,54 @@
+import java.io.File
+import java.math.BigInteger
+import kotlin.system.measureTimeMillis
+
+fun main() {
+	val initialConfiguration = File("input/1.txt").readLines()
+		.single()
+		.split(',')
+		.map(String::toInt)
+	
+	println("(Took ${measureTimeMillis { part1(initialConfiguration) }} ms)")
+	println("(Took ${measureTimeMillis { part2(initialConfiguration) }} ms)")
+}
+
+class FishConfiguration(initialConfiguration: List<Int>) {
+	private var fishCountByAge = Array(9) { age -> initialConfiguration.count { it == age }.toBigInteger() }
+	private var day = 0
+	
+	private val totalFish
+		get() = fishCountByAge.fold(BigInteger.ZERO, BigInteger::add)
+	
+	fun advance(days: Int) {
+		for (day in 1..days) {
+			advanceToNextDay()
+		}
+	}
+	
+	private fun advanceToNextDay() {
+		val newCountByAge = Array(9) { BigInteger.ZERO}
+		
+		for ((age, count) in fishCountByAge.withIndex()) {
+			if (age == 0) {
+				newCountByAge[6] += count
+				newCountByAge[8] += count
+			}
+			else {
+				newCountByAge[age - 1] += count
+			}
+		}
+		
+		fishCountByAge = newCountByAge
+		++day
+		
+		println("Day ${day.toString().padStart(3)}: $totalFish fish")
+	}
+}
+
+fun part1(initialConfiguration: List<Int>) {
+	FishConfiguration(initialConfiguration).advance(80)
+}
+
+fun part2(initialConfiguration: List<Int>) {
+	FishConfiguration(initialConfiguration).advance(256)
+}

README.md

@@ -35,3 +35,4 @@ The versions should not matter, but I used Visual Studio 2019 with `MSVC v142 (1
 | 2021 |  03 | Kotlin   |
 | 2021 |  04 | Kotlin   |
 | 2021 |  05 | Kotlin   |
+| 2021 |  06 | Kotlin   |

build.gradle.kts

@@ -48,4 +48,5 @@ sourceSets {
 	make(2021, 3)
 	make(2021, 4)
 	make(2021, 5)
+	make(2021, 6)
 }