Solve day 22

Author: Mistborn94

src/main/kotlin/day22/Day22.kt

@@ -0,0 +1,45 @@
+package day22
+
+import helper.Debug
+
+fun solveA(text: String, debug: Debug = Debug.Disabled): Long {
+    return text.lines().sumOf {
+        val seed = it.toLong()
+        val last = sequenceA(seed).last()
+        debug {
+            println("$seed -> $last")
+        }
+        last
+    }
+}
+
+fun Long.mix(next: Long): Long = xor(next)
+fun Long.prune() = this % 16777216
+
+fun sequenceA(start: Long): Sequence<Long> {
+    return generateSequence(start) { current ->
+        val first = (current * 64).mix(current).prune()
+        val second = (first / 32).mix(first).prune()
+        val third = (second * 2048).mix(second).prune()
+        third
+    }.take(2001)
+}
+
+fun sequenceB(start: Long) = sequenceA(start)
+    .map { "$it".last().digitToInt() }
+    .zipWithNext { a, b -> b to (b - a) }
+    .windowed(4) { list -> list.map { it.second } to list.last().first }
+
+fun solveB(text: String, debug: Debug = Debug.Disabled): Int {
+    val (bestSequence, bestValue) = text.lines().asSequence()
+        .flatMap { sequenceB(it.toLong()).distinctBy { (d, _) -> d } }
+        .groupingBy { (d, _) -> d }.fold(
+            initialValueSelector = { _, _ -> 0 },
+            operation = { _, acc, (_, count) -> acc + count }
+        ).maxBy { it.value }
+
+    debug {
+        println(bestSequence)
+    }
+    return bestValue
+}

src/main/resources/inputs

@@ -0,0 +1,79 @@
+package day22
+
+import helper.Debug
+import helper.readDayFile
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+
+internal class Day22KtTest {
+
+    private val day = 22
+
+    @Test
+    fun sample1() {
+        val text = """
+        1
+        10
+        100
+        2024
+        """.trimIndent().trimEnd()
+
+        assertEquals(37327623, solveA(text, Debug.Enabled))
+    }
+
+    @Test
+    fun sample3() {
+        val text = """
+        1
+        2
+        3
+        2024
+        """.trimIndent().trimEnd()
+
+        assertEquals(23, solveB(text, Debug.Enabled))
+    }
+
+    @Test
+    fun sample2() {
+
+        val expectedSequence = """
+            15887950
+            16495136
+            527345
+            704524
+            1553684
+            12683156
+            11100544
+            12249484
+            7753432
+            5908254""".trimIndent()
+        val expectedA = expectedSequence.lines().map { it.toLong() }
+        assertEquals(expectedA, sequenceA(123L).drop(1).take(10).toList())
+
+        val expectedB = listOf(
+            listOf(-3, 6, -1, -1) to 4,
+            listOf(6, -1, -1, 0) to 4,
+            listOf(-1, -1, 0, 2) to 6,
+            listOf(-1, 0, 2, -2) to 4,
+            listOf(0, 2, -2, 0) to 4,
+            listOf(2, -2, 0, -2) to 2,
+        )
+
+        assertEquals(expectedB, sequenceB(123L).take(6).toList())
+    }
+
+    @Test
+    fun solve() {
+        val lines = readDayFile(day, "input").readText().trimEnd()
+
+        val solveA = solveA(lines)
+        println("A: $solveA")
+        assertEquals(17262627539, solveA)
+
+        val solveB = solveB(lines)
+        println("B: $solveB")
+        //not 2121
+        assertEquals(1986, solveB)
+    }
+}