feat: day 13

2015/Day13.scala

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+package day13
+
+import scala.io.Source.fromFile
+import scala.util.chaining.*
+
+type Score = Map[String, Map[String, Int]]
+
+def parse(input: String) = input match
+  case s"$from would gain $n happiness units by sitting next to $to." =>
+    from -> (to -> n.toInt)
+  case s"$from would lose $n happiness units by sitting next to $to." =>
+    from -> (to -> -n.toInt)
+
+def parseToMap(xs: Iterable[String]) = xs
+  .map(parse)
+  .toSeq
+  .groupBy(_._1)
+  .view
+  .mapValues(_.map(_._2).toMap)
+  .toMap
+
+extension [A](xs: Seq[A])
+  def slidingCyclic(size: Int) =
+    xs.concat(xs).sliding(size).take(xs.size)
+
+  def permutationsCyclic =
+    xs.drop(1).permutations.map(xs.head +: _)
+
+def score(comb: Seq[String])(implicit scores: Score) =
+  comb
+    .slidingCyclic(3)
+    .collect { case Seq(left, center, right) =>
+      val f = scores.getOrElse(center, Map.empty)
+      f.getOrElse(left, 0) + f.getOrElse(right, 0)
+    }
+    .sum
+
+def part1(scores: Score) =
+  val people = scores.keys.toSeq
+  val combination = people.permutationsCyclic.toSeq
+
+  given Score = scores
+  combination.map(score).max
+
+def part2(scores: Score) =
+  val people = scores.keys.toSeq :+ "Me"
+  val combination = people.permutationsCyclic.toSeq
+
+  given Score = scores
+  combination.map(score).max
+
+@main def main() =
+  val scores: Score = fromFile(".cache/13.txt").getLines.toSeq.pipe(parseToMap)
+
+  println(part1(scores))
+  println(part2(scores))

2015/Day13.test.scala

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+import scala.util.chaining.*
+import munit.FunSuite
+import day13.*
+
+class Day13Tests extends FunSuite:
+  test("Part 1"):
+    val scores = """
+      Alice would gain 54 happiness units by sitting next to Bob.
+      Alice would lose 79 happiness units by sitting next to Carol.
+      Alice would lose 2 happiness units by sitting next to David.
+      Bob would gain 83 happiness units by sitting next to Alice.
+      Bob would lose 7 happiness units by sitting next to Carol.
+      Bob would lose 63 happiness units by sitting next to David.
+      Carol would lose 62 happiness units by sitting next to Alice.
+      Carol would gain 60 happiness units by sitting next to Bob.
+      Carol would gain 55 happiness units by sitting next to David.
+      David would gain 46 happiness units by sitting next to Alice.
+      David would lose 7 happiness units by sitting next to Bob.
+      David would gain 41 happiness units by sitting next to Carol.
+      """.trim.split("\n").map(_.trim).toSeq.pipe(parseToMap)
+
+    assertEquals(part1(scores), 330)