Added Strongly Connected Components

Author: S-M-J-I

src/strongly_connected_components/kosaraju/DepthFirstOrder.java

@@ -0,0 +1,33 @@
+package strongly_connected_components.kosaraju;
+
+import java.util.Stack;
+
+public class DepthFirstOrder {
+ private Stack<Vertex> stack;
+
+ public DepthFirstOrder(Graph graph) {
+ stack = new Stack<>();
+
+ for(Vertex vertex : graph.getVertices()) {
+ if( !vertex.isVisited() ) {
+ dfs(vertex);
+ }
+ }
+ }
+
+ private void dfs(Vertex vertex) {
+ vertex.setVisited(true);
+
+ for(Vertex v : vertex.getAdjList()) {
+ if(!v.isVisited()) {
+ dfs(v);
+ }
+ }
+
+ stack.push(vertex);
+ }
+
+ public Stack<Vertex> getReversePostOrder() {
+ return this.stack;
+ }
+}

src/strongly_connected_components/kosaraju/Edge.java

@@ -0,0 +1,37 @@
+package strongly_connected_components.kosaraju;
+
+public class Edge {
+ private double weight;
+ private Vertex startVertex;
+ private Vertex targetVertex;
+
+ public Edge(double weight, Vertex startVertex, Vertex targetVertex) {
+ this.weight = weight;
+ this.startVertex = startVertex;
+ this.targetVertex = targetVertex;
+ }
+
+ public double getWeight() {
+ return weight;
+ }
+
+ public void setWeight(double weight) {
+ this.weight = weight;
+ }
+
+ public Vertex getStartVertex() {
+ return startVertex;
+ }
+
+ public void setStartVertex(Vertex startVertex) {
+ this.startVertex = startVertex;
+ }
+
+ public Vertex getTargetVertex() {
+ return targetVertex;
+ }
+
+ public void setTargetVertex(Vertex targetVertex) {
+ this.targetVertex = targetVertex;
+ }
+}

src/strongly_connected_components/kosaraju/Graph.java

@@ -0,0 +1,54 @@
+package strongly_connected_components.kosaraju;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Graph {
+ private List<Vertex> vertices;
+ private List<Edge> edges;
+
+ public Graph() {
+ this.vertices = new ArrayList<>();
+ this.edges = new ArrayList<>();
+ }
+
+ public Graph(List<Vertex> vertices, List<Edge> edges) {
+ this.vertices = vertices;
+ this.edges = edges;
+ }
+
+ public List<Vertex> getVertices() {
+ return vertices;
+ }
+
+ public void setVertices(List<Vertex> vertices) {
+ this.vertices = vertices;
+ }
+
+ public List<Edge> getEdges() {
+ return edges;
+ }
+
+ public void setEdges(List<Edge> edges) {
+ this.edges = edges;
+ }
+
+ public Graph transposeGraph() {
+ Graph transpose = new Graph();
+
+ List<Vertex> transposeVertices = new ArrayList<>(this.vertices);
+
+ for(Edge edge : this.edges) {
+ /** Reverse the edges */
+ Vertex target = edge.getTargetVertex();
+ Vertex start = edge.getStartVertex();
+ int indexOfEdge = transposeVertices.indexOf(target);
+ transposeVertices.get(indexOfEdge).addNeighbours(start);
+ }
+
+ transpose.setVertices(transposeVertices);
+
+ return transpose;
+ }
+
+}

src/strongly_connected_components/kosaraju/KosarajuAlgorithm.java

@@ -0,0 +1,39 @@
+package strongly_connected_components.kosaraju;
+
+public class KosarajuAlgorithm {
+ private int[] id; // id[V] = id of SCC of the given V (vertex)
+ private int count; // no. of SCC
+ private boolean[] marked;
+
+ public KosarajuAlgorithm(Graph graph) {
+
+ DepthFirstOrder dfs = new DepthFirstOrder(graph.transposeGraph());
+
+ marked = new boolean[graph.getVertices().size()];
+ id = new int[graph.getVertices().size()];
+
+ for(Vertex vertex : dfs.getReversePostOrder()) {
+ if(!marked[vertex.getId()]) {
+ dfs(vertex);
+ count++;
+ }
+ }
+ }
+
+ private void dfs(Vertex vertex) {
+ marked[vertex.getId()] = true;
+ id[vertex.getId()] = count;
+ vertex.setComponentID(count);
+
+ for(Vertex v : vertex.getAdjList()) {
+ if(!marked[v.getId()]) {
+ dfs(v);
+ }
+ }
+ }
+
+ public int getCount() {
+ return count;
+ }
+
+}

src/strongly_connected_components/kosaraju/RunKosaraju.java

@@ -0,0 +1,52 @@
+package strongly_connected_components.kosaraju;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class RunKosaraju {
+
+ public static void main(String[] args) {
+ List<Vertex> vertexList = new ArrayList<>();
+
+ vertexList.add(new Vertex(0, "A"));
+ vertexList.add(new Vertex(1, "B"));
+ vertexList.add(new Vertex(2, "C"));
+ vertexList.add(new Vertex(3, "D"));
+ vertexList.add(new Vertex(4, "E"));
+ vertexList.add(new Vertex(5, "F"));
+ vertexList.add(new Vertex(6, "G"));
+ vertexList.add(new Vertex(7, "H"));
+
+ List<Edge> edgeList = new ArrayList<>();
+
+ edgeList.add(new Edge(1, vertexList.get(0), vertexList.get(1)));
+
+ edgeList.add(new Edge(1, vertexList.get(1), vertexList.get(4)));
+ edgeList.add(new Edge(1, vertexList.get(1), vertexList.get(5)));
+ edgeList.add(new Edge(1, vertexList.get(1), vertexList.get(2)));
+
+
+ edgeList.add(new Edge(1, vertexList.get(2), vertexList.get(6)));
+ edgeList.add(new Edge(1, vertexList.get(2), vertexList.get(3)));
+
+ edgeList.add(new Edge(1, vertexList.get(3), vertexList.get(2)));
+ edgeList.add(new Edge(1, vertexList.get(3), vertexList.get(7)));
+
+ edgeList.add(new Edge(1, vertexList.get(4), vertexList.get(0)));
+ edgeList.add(new Edge(1, vertexList.get(4), vertexList.get(5)));
+
+ edgeList.add(new Edge(1, vertexList.get(5), vertexList.get(6)));
+
+ edgeList.add(new Edge(1, vertexList.get(6), vertexList.get(5)));
+
+ edgeList.add(new Edge(1, vertexList.get(7), vertexList.get(3)));
+ edgeList.add(new Edge(1, vertexList.get(7), vertexList.get(6)));
+
+ KosarajuAlgorithm kosarajuAlgorithm = new KosarajuAlgorithm(new Graph(vertexList, edgeList));
+ System.out.println(kosarajuAlgorithm.getCount());
+
+ for(Vertex vertex : vertexList) {
+ System.out.println(vertex.getName()+": "+vertex.getComponentID());
+ }
+ }
+}

src/strongly_connected_components/kosaraju/Vertex.java

@@ -0,0 +1,70 @@
+package strongly_connected_components.kosaraju;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class Vertex {
+ private int id;
+ private String name;
+ private boolean visited;
+ private List<Vertex> adjList;
+ private int componentID;
+
+ public Vertex(int id, String name) {
+ this.id = id;
+ this.name = name;
+ this.visited = false;
+ this.adjList = new ArrayList<>();
+ }
+
+ public int getId() {
+ return id;
+ }
+
+ public void setId(int id) {
+ this.id = id;
+ }
+
+ public String getName() {
+ return name;
+ }
+
+ public void setName(String name) {
+ this.name = name;
+ }
+
+ public boolean isVisited() {
+ return visited;
+ }
+
+ public void setVisited(boolean visited) {
+ this.visited = visited;
+ }
+
+ public List<Vertex> getAdjList() {
+ return adjList;
+ }
+
+ public void setAdjList(List<Vertex> adjList) {
+ this.adjList = adjList;
+ }
+
+ public int getComponentID() {
+ return componentID;
+ }
+
+ public void setComponentID(int componentID) {
+ this.componentID = componentID;
+ }
+
+ public void addNeighbours(Vertex ...vertices) {
+ adjList.addAll(Arrays.asList(vertices));
+ }
+
+ @Override
+ public String toString() {
+ return this.name;
+ }
+
+}