added topoSort

Author: JakubSchwenkbeck

src/main/scala/algorithms/graph/TopoSort.scala

@@ -0,0 +1,42 @@
+package algorithms.graph
+
+import datastructures.graph._
+import scala.collection.mutable
+
+//Kahns Algorithm
+def topologicalSort[T](graph : Graph[T]) : Option[List[T]] =  {
+
+  val inDegree = mutable.Map[T, Int]().withDefaultValue(0)
+
+    for ((src, neighbors) <- graph.adjacencyList) {
+      for ((dest, _) <- neighbors) {
+        inDegree.update(dest, inDegree(dest) + 1)
+      }
+    }
+
+    //  Initialize queue with nodes having in-degree 0
+    val queue = mutable.Queue[T]()
+    for (vertex <- graph.adjacencyList.keys if inDegree(vertex) == 0) {
+      queue.enqueue(vertex)
+    }
+
+    val sortedList = mutable.ListBuffer[T]()
+
+    //  Process queue
+    while (queue.nonEmpty) {
+      val vertex = queue.dequeue()
+      sortedList.append(vertex)
+
+      for ((neighbor, _) <- graph.adjacencyList(vertex)) {
+        inDegree.update(neighbor, inDegree(neighbor) - 1)
+        if (inDegree(neighbor) == 0) {
+          queue.enqueue(neighbor)
+        }
+      }
+    }
+
+    //  Cycle check
+    if (sortedList.size == graph.adjacencyList.size) Some(sortedList.toList) else None
+}
+
+

src/main/scala/datastructures/graph/graph.scala

@@ -5,8 +5,8 @@ import scala.collection.mutable
 case class Edge[T](src: T, dest: T, weight: Double)
 
 class Graph[T](val isDirected: Boolean) {
-  private val adjacencyList: mutable.Map[T, mutable.ListBuffer[(T, Double)]] = mutable.Map()
-  private val edges: mutable.ListBuffer[Edge[T]] = mutable.ListBuffer()
+  val adjacencyList: mutable.Map[T, mutable.ListBuffer[(T, Double)]] = mutable.Map()
+  val edges: mutable.ListBuffer[Edge[T]] = mutable.ListBuffer()
 
   def addVertex(vertex: T): Unit = {
     adjacencyList.getOrElseUpdate(vertex, mutable.ListBuffer())