Day 5

Author: WVerlaek

src/main/kotlin/y24/Day5.kt

@@ -0,0 +1,66 @@
+package y24
+
+import common.puzzle.solvePuzzle
+import common.puzzle.Input
+import common.puzzle.Puzzle
+import common.datastructures.*
+import common.ext.*
+import common.puzzle.splitToInts
+import common.util.*
+import java.util.*
+import kotlin.math.*
+import kotlin.system.exitProcess
+
+
+fun main() = solvePuzzle(year = 2024, day = 5) { Day5(it) }
+
+class Day5(val input: Input) : Puzzle {
+
+    data class PageRule(
+        val before: Int,
+        val after: Int,
+    )
+
+    data class Update(
+        val pageNumbers: List<Int>,
+    ) {
+        val middle = pageNumbers[pageNumbers.size / 2]
+
+        fun satisfies(rules: List<PageRule>): Boolean {
+            val pageIndices = pageNumbers.mapIndexed { index, i -> i to index }.toMap()
+            return rules.all { (before, after) ->
+                val beforeIndex = pageIndices[before] ?: return@all true
+                val afterIndex = pageIndices[after] ?: return@all true
+                beforeIndex < afterIndex
+            }
+        }
+
+        fun sortedBy(rules: List<PageRule>): Update {
+            val sorted = pageNumbers.sortedWith(Comparator { p1, p2 ->
+                val rule = rules.find { (it.before == p1 && it.after == p2) || (it.before == p2 && it.after == p1) }
+                    ?: return@Comparator 0
+
+                if (rule.before == p1) -1 else 1
+            })
+
+            return Update(sorted)
+        }
+    }
+
+    private val emptyLine = input.lines.indexOf("")
+    private val rules = input.lines.subList(0, emptyLine).map { line ->
+        val (before, after) = line.splitToInts("|")
+        PageRule(before, after)
+    }
+    private val updates = input.lines.subList(emptyLine + 1, input.lines.size).map { line ->
+        val pageNumbers = line.splitToInts(",")
+        Update(pageNumbers)
+    }
+
+    override fun solveLevel1(): Any {
+        return updates.filter { it.satisfies(rules) }.sumOf { it.middle }
+    }
+    override fun solveLevel2(): Any {
+        return updates.filter { !it.satisfies(rules) }.map { it.sortedBy(rules) }.sumOf { it.middle }
+    }
+}

src/test/kotlin/y24/Day5Test.kt

@@ -0,0 +1,50 @@
+package y24
+
+import common.puzzle.Input
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+
+internal class Day5Test {
+    private val sample = Input("""
+    47|53
+    97|13
+    97|61
+    97|47
+    75|29
+    61|13
+    75|53
+    29|13
+    97|29
+    53|29
+    61|53
+    97|53
+    61|29
+    47|13
+    75|47
+    97|75
+    47|61
+    75|61
+    47|29
+    75|13
+    53|13
+    
+    75,47,61,53,29
+    97,61,53,29,13
+    75,29,13
+    75,97,47,61,53
+    61,13,29
+    97,13,75,29,47
+    """.trimIndent())
+
+    private val day = Day5(sample)
+
+    @Test
+    fun solveLevel1() {
+        assertEquals(143, day.solveLevel1())
+    }
+
+    @Test
+    fun solveLevel2() {
+         assertEquals(123, day.solveLevel2())
+    }
+}