Day 22 2024

src/main/kotlin/me/peckb/aoc/_2024/calendar/day22/Day22.kt

@@ -0,0 +1,70 @@
+package me.peckb.aoc._2024.calendar.day22
+
+import arrow.core.Tuple4
+import javax.inject.Inject
+import me.peckb.aoc.generators.InputGenerator.InputGeneratorFactory
+
+class Day22 @Inject constructor(
+  private val generatorFactory: InputGeneratorFactory,
+) {
+  fun partOne(filename: String) = generatorFactory.forFile(filename).readAs(::secretNumber) { input ->
+    input.sumOf { number ->
+      (0 until 2000).fold(number) { n, _ -> nextNumber(n) }
+    }
+  }
+
+  fun partTwo(filename: String) = generatorFactory.forFile(filename).readAs(::secretNumber) { input ->
+    val data = input.toList()
+
+    val solutions = mutableMapOf<Tuple4<Long, Long, Long, Long>, Long>()
+
+    data.forEach { number->
+      val buyerNumbers = sequence {
+        var n = number
+        while (true) {
+          yield(n)
+          n = nextNumber(n)
+        }
+      }
+
+      val mySequences = mutableSetOf<Tuple4<Long, Long, Long, Long>>()
+
+      buyerNumbers
+        .map { it % 10 }
+        .windowed(5)
+        .take(2000)
+        .forEach { (a, b, c, d, e) ->
+          val k = Tuple4(b - a, c - b, d - c, e - d)
+          if (k !in mySequences) {
+            solutions.merge(k, e, Long::plus)
+            mySequences.add(k)
+          }
+        }
+    }
+
+    solutions.values.max()
+  }
+
+  private fun nextNumber(number: Long): Long {
+    var n = number
+
+    // step one
+    val a = n * 64   // Calculate the result of multiplying the secret number by 64.
+    n = n xor a      // Then, mix this result into the secret number.
+    n %= 16_777_216  // Finally, prune the secret number.
+
+    // step two
+    val b = n / 32   // Calculate the result of dividing the secret number by 32.
+    n = n xor b      // Then, mix this result into the secret number.
+    n %= 16_777_216  // Finally, prune the secret number.
+
+    // step three
+    val c = n * 2048 // Calculate the result of multiplying the secret number by 2048.
+    n = n xor c      // Then, mix this result into the secret number.
+    n %= 16_777_216  // Finally, prune the secret number.
+
+    return n
+  }
+
+  private fun secretNumber(line: String) = line.toLong()
+}

src/main/kotlin/me/peckb/aoc/_2024/calendar/day22/README.md

@@ -0,0 +1 @@
+## [Day 22: Monkey Market](https://adventofcode.com/2024/day/22)

src/test/kotlin/me/peckb/aoc/_2024/TestDayComponent.kt

@@ -21,6 +21,7 @@ import me.peckb.aoc._2024.calendar.day18.Day18Test
 import me.peckb.aoc._2024.calendar.day19.Day19Test
 import me.peckb.aoc._2024.calendar.day20.Day20Test
 import me.peckb.aoc._2024.calendar.day21.Day21Test
+import me.peckb.aoc._2024.calendar.day22.Day22Test
 import javax.inject.Singleton
 import me.peckb.aoc.DayComponent
 import me.peckb.aoc.InputModule
@@ -50,4 +51,5 @@ internal interface TestDayComponent : DayComponent {
   fun inject(day19Test: Day19Test)
   fun inject(day20Test: Day20Test)
   fun inject(day21Test: Day21Test)
+  fun inject(day22Test: Day22Test)
 }

src/test/kotlin/me/peckb/aoc/_2024/calendar/day22/Day22Test.kt

@@ -0,0 +1,32 @@
+package me.peckb.aoc._2024.calendar.day22
+
+import javax.inject.Inject
+
+import me.peckb.aoc._2024.DaggerTestDayComponent
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Test
+
+internal class Day22Test {
+  @Inject
+  lateinit var day22: Day22
+
+  @BeforeEach
+  fun setup() {
+    DaggerTestDayComponent.create().inject(this)
+  }
+
+  @Test
+  fun testDay22PartOne() {
+    assertEquals(16039090236, day22.partOne(DAY_22))
+  }
+
+  @Test
+  fun testDay22PartTwo() {
+    assertEquals(1808, day22.partTwo(DAY_22))
+  }
+
+  companion object {
+    private const val DAY_22: String = "advent-of-code-input/2024/day22.input"
+  }
+}