Day 14

src/main/kotlin/com/basdado/adventofcode/Day14.kt

@@ -0,0 +1,98 @@
+package com.basdado.adventofcode
+
+const val DAY14_INPUT = "/day/14/input.txt"
+
+fun main() {
+    val day = Day14()
+    day.puzzle1()
+    day.puzzle2()
+}
+
+class Day14 {
+
+    fun puzzle1() {
+
+        val recipeCount = lines(DAY14_INPUT).findFirst().get().toInt()
+        val initialRecipes = listOf<Byte>(3, 7)
+        val recipes = initialRecipes.toMutableList()
+
+        var elf1Pos = 0
+        var elf2Pos = 1
+
+        while(recipes.size < recipeCount + 10) {
+
+            val elf1Score = recipes[elf1Pos]
+            val elf2Score = recipes[elf2Pos]
+            appendDigits(elf1Score + elf2Score, recipes)
+
+            elf1Pos = (elf1Pos + 1 + elf1Score) % recipes.size
+            elf2Pos = (elf2Pos + 1 + elf2Score) % recipes.size
+        }
+
+        println(recipes.subList(recipeCount, recipeCount + 10).joinToString(""))
+    }
+
+    fun puzzle2() {
+
+        val desiredRecipeSequence = getDigits(lines(DAY14_INPUT).findFirst().get().toLong())
+        val initialRecipes = listOf<Byte>(3, 7)
+        val recipes = initialRecipes.toMutableList()
+
+        println(findRecipeSequence(recipes, desiredRecipeSequence))
+    }
+
+    private fun findRecipeSequence(
+        recipes: MutableList<Byte>,
+        desiredRecipeSequence: List<Byte>
+    ): Int {
+        var elf1Pos = 0
+        var elf2Pos = 1
+
+        while (true) {
+
+            val elf1Score = recipes[elf1Pos]
+            val elf2Score = recipes[elf2Pos]
+            val newRecipeScores = elf1Score + elf2Score
+
+            appendDigits(newRecipeScores, recipes)
+
+            if (newRecipeScores >= 10) {
+                if (subListEquals(recipes.size - desiredRecipeSequence.size - 1, recipes, desiredRecipeSequence)) {
+                    return recipes.size - desiredRecipeSequence.size - 1
+                }
+            }
+            if (subListEquals(recipes.size - desiredRecipeSequence.size, recipes, desiredRecipeSequence)) {
+                return recipes.size - desiredRecipeSequence.size
+            }
+
+            elf1Pos = (elf1Pos + 1 + elf1Score) % recipes.size
+            elf2Pos = (elf2Pos + 1 + elf2Score) % recipes.size
+        }
+    }
+
+    private fun <T> subListEquals(startIndex: Int, fullList: List<T>, subList: List<T>): Boolean {
+
+        if (startIndex < 0 || startIndex + subList.size > fullList.size) {
+            return false
+        }
+        for (i in 0 until subList.size) {
+            if (fullList[startIndex + i] != subList[i]) {
+                return false
+            }
+        }
+        return true
+    }
+
+    private fun appendDigits(n: Int, list: MutableList<Byte>) {
+        when (n) {
+            in 1..9 -> list.add(n.toByte())
+            in 10..19 -> {
+                list.add((n / 10).toByte())
+                list.add((n % 10).toByte())
+            }
+            else -> list.addAll(getDigits(n.toLong()))
+        }
+    }
+
+    private fun getDigits(n: Long): List<Byte> = n.toString().split("").filter { !it.isBlank() }.map { it.toByte() }
+}

src/main/kotlin/com/basdado/adventofcode/Day9.kt

@@ -13,7 +13,7 @@ fun main() {
     println("Puzzle 1 time: " + measureTimeMillis { day.puzzle1() } + " ms")
     // Puzzle 1 answer = 385820
     // Let's do 10 runs
-    println("Puzzle 2 time: " + (1..10).map {measureTimeMillis { day.puzzle2() }}.average() + " ms")
+    println("Puzzle 2 time: " + (1..10).map { measureTimeMillis { day.puzzle2() } }.average() + " ms")
 }
 
 class Day9 {

src/main/resources/day/14/example.txt

@@ -0,0 +1 @@
+37

src/main/resources/day/14/input.txt

@@ -0,0 +1 @@
+209231