VertexCover.java

VertexCover.java

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+// Java Program to print Vertex Cover of a given undirected graph 
+import java.io.*; 
+import java.util.*; 
+import java.util.LinkedList; 
+
+// This class represents an undirected graph using adjacency list 
+class Graph 
+{ 
+	private int V; // No. of vertices 
+
+	// Array of lists for Adjacency List Representation 
+	private LinkedList<Integer> adj[]; 
+
+	// Constructor 
+	Graph(int v) 
+	{ 
+		V = v; 
+		adj = new LinkedList[v]; 
+		for (int i=0; i<v; ++i) 
+			adj[i] = new LinkedList(); 
+	} 
+
+	//Function to add an edge into the graph 
+	void addEdge(int v, int w) 
+	{ 
+		adj[v].add(w); // Add w to v's list. 
+		adj[w].add(v); //Graph is undirected 
+	} 
+
+	// The function to print vertex cover 
+	void printVertexCover() 
+	{ 
+		// Initialize all vertices as not visited. 
+		boolean visited[] = new boolean[V]; 
+		for (int i=0; i<V; i++) 
+			visited[i] = false; 
+
+		Iterator<Integer> i; 
+
+		// Consider all edges one by one 
+		for (int u=0; u<V; u++) 
+		{ 
+			// An edge is only picked when both visited[u] 
+			// and visited[v] are false 
+			if (visited[u] == false) 
+			{ 
+				// Go through all adjacents of u and pick the 
+				// first not yet visited vertex (We are basically 
+				// picking an edge (u, v) from remaining edges. 
+				i = adj[u].iterator(); 
+				while (i.hasNext()) 
+				{ 
+					int v = i.next(); 
+					if (visited[v] == false) 
+					{ 
+						// Add the vertices (u, v) to the result 
+						// set. We make the vertex u and v visited 
+						// so that all edges from/to them would 
+						// be ignored 
+						visited[v] = true; 
+						visited[u] = true; 
+						break; 
+					} 
+				} 
+			} 
+		} 
+
+		// Print the vertex cover 
+		for (int j=0; j<V; j++) 
+			if (visited[j]) 
+			System.out.print(j+" "); 
+	} 
+
+	// Driver method 
+	public static void main(String args[]) 
+	{ 
+		// Create a graph given in the above diagram 
+		Graph g = new Graph(7); 
+		g.addEdge(0, 1); 
+		g.addEdge(0, 2); 
+		g.addEdge(1, 3); 
+		g.addEdge(3, 4); 
+		g.addEdge(4, 5); 
+		g.addEdge(5, 6); 
+
+		g.printVertexCover(); 
+	} 
+} 
+// This code is contributed by Aakash Hasija