Day 3: Mull It Over

README.md

@@ -7,6 +7,7 @@ Advent of Code is an Advent calendar of small programming puzzles by [Eric Wastl
 
 - Day 1: [Historian Hysteria](https://adventofcode.com/2024/day/1) -- [Day1.kt](https://github.com/andilau/advent-of-code-2024/blob/main/src/main/kotlin/days/Day1.kt)
 - Day 2: [Red-Nosed Reports](https://adventofcode.com/2024/day/2) -- [Day2.kt](https://github.com/andilau/advent-of-code-2024/blob/main/src/main/kotlin/days/Day2.kt)
+- Day 3: [Mull It Over](https://adventofcode.com/2024/day/3) -- [Day3.kt](https://github.com/andilau/advent-of-code-2024/blob/main/src/main/kotlin/days/Day3.kt)
 
 ### Features
 

src/main/kotlin/days/Day3.kt

@@ -0,0 +1,36 @@
+package days
+
+@AdventOfCodePuzzle(
+    name = "Mull It Over",
+    url = "https://adventofcode.com/2024/day/3",
+    date = Date(day = 3, year = 2024)
+)
+class Day3(val memory: List<String>) : Puzzle {
+
+    val regex = """mul\((\d{1,3}+),(\d{1,3}+)\)""".toRegex()
+    val regex2 = """mul\((\d{1,3}+),(\d{1,3}+)\)|(do\(\))|(don't\(\))""".toRegex()
+
+    override fun partOne(): Int = regex
+        .findAll(memory.joinToString())
+        .map { it.groupValues.drop(1).map { it.toInt() }.fold(1) { a, b -> a * b } }
+        .sum()
+
+    override fun partTwo(): Int = regex2
+        .findAll(memory.joinToString())
+        .map {
+            val what = it.groupValues.first()
+            when (what) {
+                "do()" -> 1 to 0
+                "don't()" -> 0 to 0
+                else -> 1 to it.groupValues.drop(1).take(2).map { it.toInt() }.fold(1) { a, b -> a * b }
+            }
+        }
+        .fold(1 to 0) { acc, p ->
+            Pair(
+                if (p.second == 0) p.first else acc.first,
+                acc.second + acc.first * p.second
+            )
+        }
+        .second
+
+}