Day 5: Print Queue (#5)

README.md

@@ -9,6 +9,7 @@ Advent of Code is an Advent calendar of small programming puzzles by [Eric Wastl
 - 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)
 - Day 4: [Ceres Search](https://adventofcode.com/2024/day/4) -- [Day4.kt](https://github.com/andilau/advent-of-code-2024/blob/main/src/main/kotlin/days/Day4.kt)
+- Day 5: [Print Queue](https://adventofcode.com/2024/day/5) -- [Day4.kt](https://github.com/andilau/advent-of-code-2024/blob/main/src/main/kotlin/days/Day5.kt)
 
 ### Features
 

settings.gradle

@@ -1 +1 @@
-rootProject.name = 'advent-of-code-starter'
+rootProject.name = 'advent-of-code-2024'

src/main/kotlin/days/Day5.kt

@@ -0,0 +1,47 @@
+package days
+
+@AdventOfCodePuzzle(
+    name = "Print Queue",
+    url = "https://adventofcode.com/2024/day/5",
+    date = Date(day = 5, year = 2024)
+)
+class Day5(input: List<String>) : Puzzle {
+
+    private val pageOrderingRules = input
+        .takeWhile { it.isNotEmpty() }
+        .map { line -> line.split('|').let { it[0].toInt() to it[1].toInt() } }
+    private val pageToProduce = input
+        .dropWhile { it.isNotEmpty() }
+        .drop(1)
+        .map { it.split(',').map { it.toInt() } }
+
+    override fun partOne(): Int = pageToProduce
+        .filter { pages -> validOrder(pages) }
+        .sumOf(::middlePage)
+
+    override fun partTwo() = pageToProduce
+        .filterNot { pages -> validOrder(pages) }
+        .map { pages -> reorder(pages) }
+        .sumOf { middlePage(it) }
+
+    private fun reorder(pages: List<Int>): List<Int> {
+        val selectedRules = pageOrderingRules.filter { (prev, next) -> prev in pages && next in pages }
+        val eachCount = selectedRules.groupingBy { it.first }.eachCount().toMutableMap()
+        selectedRules.map { it.second }.forEach { eachCount.putIfAbsent(it, 0) }
+
+        return eachCount
+            .map { (page, degree) -> degree to page }
+            .toMap()
+            .toSortedMap(Comparator.naturalOrder<Int?>().reversed())
+            .values.toList()
+    }
+
+    private fun validOrder(pages: List<Int>): Boolean {
+        return pageOrderingRules
+            .filter { (prev, next) -> prev in pages && next in pages }
+            .all { (prev, next) -> pages.indexOf(prev) < pages.indexOf(next) }
+    }
+
+    private fun middlePage(it: List<Int>) = it[it.size / 2]
+
+}