Add Scala implementation

Author: zabio3

Dijkstras.scala

@@ -0,0 +1,74 @@
+import scala.collection.mutable
+
+object Dijkstras extends App {
+
+  val graphs = new SimpleGraph[String](
+    Map(
+      "A" -> Map("B" -> 7, "C" -> 8),
+      "B" -> Map("A" -> 7, "F" -> 2),
+      "C" -> Map("A" -> 8, "G" -> 4, "F" -> 6),
+      "D" -> Map("F" -> 8),
+      "E" -> Map("H" -> 1),
+      "F" -> Map("B" -> 2, "C" -> 6, "D" -> 8, "G" -> 9, "H" -> 1),
+      "G" -> Map("C" -> 4, "F" -> 9),
+      "H" -> Map("E" -> 1, "F" -> 3)
+    )
+  )
+  graphs.getShortestPath("A","E")
+}
+
+case class SimpleGraph[N](succs: Map[N, Map[N, Int]]) {
+
+  def apply(n: N) = succs.getOrElse(n, Map.empty)
+
+  def initDistance(point:N) = {
+    this.succs.foldLeft(Map.empty:Map[N, (Int, Seq[N])]) {
+      (result, vertex) =>
+        if (vertex._1 == point) {
+          result ++ Map(point -> (0,Seq(point)))
+        } else {
+          result ++ Map(vertex._1 -> (Int.MaxValue, Seq(point)))
+        }
+    }
+  }
+
+  def shortestPath(n:N)(selected:Set[N])(currentDistance:Map[N, (Int, Seq[N])]) = {
+    currentDistance.keys.filterNot(selected.contains(_)).foldLeft(n:N) {
+      (result, point) =>
+        currentDistance(point)._1 match {
+          case x if result == n => point
+          case y if (currentDistance(result)._1 > y) => point
+          case _ => result
+        }
+    }
+  }
+
+  def updateGraph(n:N)(f:N)(distance:Map[N, (Int, Seq[N])]):Map[N, (Int, Seq[N])] = {
+    val hereDistance = distance(f)
+    this.succs(f).foldLeft(distance:Map[N, (Int, Seq[N])]) {
+      (result, vertex) =>
+        val nodeDistance = hereDistance._1 match {
+          case Int.MaxValue => vertex._2
+          case _ => hereDistance._1 + vertex._2
+        }
+        if (distance(vertex._1)._1 > nodeDistance) {
+          result ++ Map(vertex._1 -> (nodeDistance, hereDistance._2 :+ vertex._1))
+        } else {
+          result
+        }
+    }
+  }
+
+  def getShortestPath(start: N, finish: N) = {
+    var nextNode:N = start;
+    var currentDistance:Map[N, (Int, Seq[N])] = initDistance(start);
+    var unreachedVertexSet:Set[N] = succs.keySet.filterNot(_ == start)
+    while (!unreachedVertexSet.isEmpty) {
+      currentDistance = updateGraph(start)(nextNode)(currentDistance)
+      nextNode = shortestPath(start)(succs.keySet.filterNot(unreachedVertexSet.contains(_)))(currentDistance) // 次のノードを決定させる
+      unreachedVertexSet = unreachedVertexSet.-(nextNode)
+    }
+    println("result : ", currentDistance(finish)._2.reverse.toSeq)
+  }
+
+}