Day 22: Monkey Market (#19)

README.md

@@ -16,6 +16,7 @@ Advent of Code is an Advent calendar of small programming puzzles by [Eric Wastl
 - Day 12: [Garden Groups](https://adventofcode.com/2024/day/12) -- [Day12.kt](https://github.com/andilau/advent-of-code-2024/blob/main/src/main/kotlin/days/Day12.kt)
 - Day 14: [Restroom Redoubt](https://adventofcode.com/2024/day/14) -- [Day14.kt](https://github.com/andilau/advent-of-code-2024/blob/main/src/main/kotlin/days/Day14.kt)
 - Day 18: [RAM Run](https://adventofcode.com/2024/day/18) -- [Day18.kt](https://github.com/andilau/advent-of-code-2024/blob/main/src/main/kotlin/days/Day18.kt)
+- Day 22: [Monkey Market](https://adventofcode.com/2024/day/22) -- [Day22.kt](https://github.com/andilau/advent-of-code-2024/blob/main/src/main/kotlin/days/Day22.kt)
 
 ### Features
 

src/main/kotlin/days/Day22.kt

@@ -0,0 +1,54 @@
+package days
+
+@AdventOfCodePuzzle(
+    name = "Monkey Market",
+    url = "https://adventofcode.com/2024/day/22",
+    date = Date(day = 22, year = 2024)
+)
+class Day22(val input: List<String>) : Puzzle {
+    val secrets = input.map { it.toInt() }
+
+    override fun partOne(): Long {
+        return secrets.sumOf { secret ->
+            generateSequence(secret) { it.next() }
+                .take(2001)
+                .last().toLong()
+        }
+    }
+
+    override fun partTwo(): Int {
+        val seqPriceSums = mutableMapOf<List<Int>, Int>()
+        secrets.forEach { secret ->
+            println("secret = ${secret}")
+            val prices: List<Int> = generateSequence(secret) { it.next() }
+                .take(2001)
+                .map { it.mod(10) }
+                .toList()
+            val sequences = prices
+                .zipWithNext { a, b -> b - a }
+                .windowed(4)
+                .toList()
+            val zip = prices.drop(4).zip(sequences)
+            val seen = mutableSetOf<List<Int>>()
+            for ((price, seq) in zip) {
+                if (seq in seen) continue
+                seen += seq
+                seqPriceSums.compute(seq) { _, v -> v?.plus(price) ?: price }
+            }
+        }
+        return seqPriceSums.values.maxOrNull() ?: 0
+    }
+
+    fun next(nums: List<Int>): List<Int> {
+        return nums.map { it.next() }
+    }
+
+    fun Int.next(): Int {
+        var x = this
+        x = x.xor(x * 64).mod(16777216)
+        x = x.xor(x / 32).mod(16777216)
+        x = x.xor(x * 2048).mod(16777216)
+        return x
+    }
+
+}