topologicalSorting.java

topologicalSorting.java

@@ -0,0 +1,91 @@
+// A Java program to print topological
+// sorting of a DAG
+import java.io.*;
+import java.util.*;
+
+// This class represents a directed graph
+// using adjacency list representation
+class Graph {
+	// No. of vertices
+	private int V;
+
+	// Adjacency List as ArrayList of ArrayList's
+	private ArrayList<ArrayList<Integer> > adj;
+
+	// Constructor
+	Graph(int v)
+	{
+		V = v;
+		adj = new ArrayList<ArrayList<Integer> >(v);
+		for (int i = 0; i < v; ++i)
+			adj.add(new ArrayList<Integer>());
+	}
+
+	// Function to add an edge into the graph
+	void addEdge(int v, int w) { adj.get(v).add(w); }
+
+	// A recursive function used by topologicalSort
+	void topologicalSortUtil(int v, boolean visited[],
+							Stack<Integer> stack)
+	{
+		// Mark the current node as visited.
+		visited[v] = true;
+		Integer i;
+
+		// Recur for all the vertices adjacent
+		// to thisvertex
+		Iterator<Integer> it = adj.get(v).iterator();
+		while (it.hasNext()) {
+			i = it.next();
+			if (!visited[i])
+				topologicalSortUtil(i, visited, stack);
+		}
+
+		// Push current vertex to stack
+		// which stores result
+		stack.push(new Integer(v));
+	}
+
+	// The function to do Topological Sort.
+	// It uses recursive topologicalSortUtil()
+	void topologicalSort()
+	{
+		Stack<Integer> stack = new Stack<Integer>();
+
+		// Mark all the vertices as not visited
+		boolean visited[] = new boolean[V];
+		for (int i = 0; i < V; i++)
+			visited[i] = false;
+
+		// Call the recursive helper
+		// function to store
+		// Topological Sort starting
+		// from all vertices one by one
+		for (int i = 0; i < V; i++)
+			if (visited[i] == false)
+				topologicalSortUtil(i, visited, stack);
+
+		// Print contents of stack
+		while (stack.empty() == false)
+			System.out.print(stack.pop() + " ");
+	}
+
+	// Driver code
+	public static void main(String args[])
+	{
+		// Create a graph given in the above diagram
+		Graph g = new Graph(6);
+		g.addEdge(5, 2);
+		g.addEdge(5, 0);
+		g.addEdge(4, 0);
+		g.addEdge(4, 1);
+		g.addEdge(2, 3);
+		g.addEdge(3, 1);
+
+		System.out.println("Following is a Topological "
+						+ "sort of the given graph");
+		// Function Call
+		g.topologicalSort();
+	}
+}
+// This code is contributed by Aakash Hasija