Day 9 solution

Author: Kalle Wuoti

day9/input.txt

@@ -0,0 +1,28 @@
+AlphaCentauri to Snowdin = 66
+AlphaCentauri to Tambi = 28
+AlphaCentauri to Faerun = 60
+AlphaCentauri to Norrath = 34
+AlphaCentauri to Straylight = 34
+AlphaCentauri to Tristram = 3
+AlphaCentauri to Arbre = 108
+Snowdin to Tambi = 22
+Snowdin to Faerun = 12
+Snowdin to Norrath = 91
+Snowdin to Straylight = 121
+Snowdin to Tristram = 111
+Snowdin to Arbre = 71
+Tambi to Faerun = 39
+Tambi to Norrath = 113
+Tambi to Straylight = 130
+Tambi to Tristram = 35
+Tambi to Arbre = 40
+Faerun to Norrath = 63
+Faerun to Straylight = 21
+Faerun to Tristram = 57
+Faerun to Arbre = 83
+Norrath to Straylight = 9
+Norrath to Tristram = 50
+Norrath to Arbre = 60
+Straylight to Tristram = 27
+Straylight to Arbre = 81
+Tristram to Arbre = 90

day9/prog.scala

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+import scala.io.Source
+import scala.util.Try
+
+val dsts = Source.fromFile("input.txt").getLines
+
+val dstR = """([A-Za-z\d]+) to ([A-Za-z\d]+) = (\d+)""".r
+case class Route(p1: String, p2: String, distance: Int)
+
+def updateRoutes(m: Map[String, Map[String, Int]], from: String, to: String, dst: Int) = m.updated(from, m.get(from).getOrElse(Map[String, Int]()).updated(to, dst))
+
+val routes = dsts.map {
+  case dstR(p1, p2, dst) => Route(p1, p2, dst.toInt)
+}.foldLeft(Map[String, Map[String, Int]]()){
+   case (acc, Route(p1, p2, dst)) => updateRoutes(updateRoutes(acc, p1, p2, dst), p2, p1, dst)
+}
+
+def findRoute(place: String, visited: List[String], dst: Int, comparator: (Int, Int) => Boolean): (List[String], Int) = {
+  routes(place).filter { case (k, _) => !visited.contains(k) && k != place } match {
+    case s if s.isEmpty => (place :: visited, dst)
+    case s => s.map { case (p, ds) => findRoute(p, place :: visited, dst + ds, comparator)}.reduceLeft((a, b) => if (comparator(a._2, b._2)) a else b)
+  }
+}
+
+def findLongestOrShortestRoute(shortest: Boolean = true) = {
+  val shortestComparator = (a: Int, b:Int) => a < b
+  val comparator = if (shortest) shortestComparator else (a: Int, b: Int) => !shortestComparator(a, b)
+  
+  routes.keys.map(p => findRoute(p, List(), 0, comparator)).reduceLeft((a, b) => if (comparator(a._2, b._2)) a else b)
+}
+
+def findShortestRoute() = findLongestOrShortestRoute(true)
+def findLongestRoute() = findLongestOrShortestRoute(false)
+
+val shortest = findShortestRoute()
+val longest = findLongestRoute()
+
+println(s"The shortest route is ${shortest._2}: ${shortest._1.mkString(", ")}")
+println(s"The longest route is ${longest._2}: ${longest._1.mkString(", ")}")