Day 05

aoc/src/dev/ctsk/aoc/Main.scala

@@ -6,7 +6,8 @@ val solvers = Map[Int, Solver](
   1 -> Day01,
   2 -> Day02,
   3 -> Day03,
-  4 -> Day04
+  4 -> Day04,
+  5 -> Day05
 )
 
 @main def main(day: String, input: String): Unit =

aoc/src/dev/ctsk/aoc/days/Day05.scala

@@ -0,0 +1,39 @@
+package dev.ctsk.aoc.days
+
+import dev.ctsk.aoc._
+
+object Day05 extends Solver(5):
+  def pre(input: String): (Set[(Int, Int)], Vector[Vector[Int]]) =
+    val Array(rulesStr, updatesStr) =
+      io.Source.fromFile(input).mkString.split("\n\n")
+
+    val rules = rulesStr.linesIterator
+      .map(rule => {
+        val Array(a, b) = rule.split("""\|""")
+        (a.toInt, b.toInt)
+      })
+      .toSet
+
+    val updates =
+      updatesStr.linesIterator.map(_.split(",").map(_.toInt).toVector).toVector
+
+    (rules, updates)
+
+  def run(input: String): (Timings, Solution) =
+    val (pre_time, (rules, updates)) = timed { pre(input) }
+
+    def isOrdered(u: Vector[Int]): Boolean =
+      !u.combinations(2).exists { case Seq(a, b) =>
+        rules.contains((b, a))
+      }
+
+    def findMiddle(u: Vector[Int]): Int =
+      u.find(e =>
+        u.count(rules.contains(_, e)) <= u.length / 2
+          && u.count(rules.contains(e, _)) <= u.length / 2
+      ).get
+
+    val p1 = timed { updates.filter(isOrdered).map(u => u(u.length / 2)).sum }
+    val p2 = timed { updates.filterNot(isOrdered).map(findMiddle).sum }
+
+    (Timings(pre_time, p1._1, p2._1), Solution(Int.box(p1._2), Int.box(p2._2)))

data/05.ans

@@ -0,0 +1,2 @@
+4637
+6370