Merge pull request #113 from vikramc54/main

Added Sieve of Eratosthenes

Author: jvm-coder

SieveOfEratosthenes.java

@@ -0,0 +1,24 @@
+// Sieve of Eratosthenes is an algorithm that finds all the primes upto a certain number.
+
+import java.util.Scanner;
+
+class SieveOfEratosthenes {
+    public static void main(String args[]) {
+        int n;
+        System.out.print("Enter a number: ");
+        Scanner sc = new Scanner(System.in);
+        n = sc.nextInt();
+        boolean composites[] = new boolean[n + 1];
+
+        for(int i = 2; i * i <= n; i++) {
+            if(!composites[i])
+                for(int j = i * i; j <= n; j+=i)
+                    composites[j] = true;
+        }
+
+        System.out.println("Primes:");
+        for(int i = 2; i <= n; i++) 
+            if(!composites[i])
+                System.out.println(i);
+    }
+}

topologicalSorting.java

@@ -1,91 +1,53 @@
-// 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>());
+class Graph{
+	int v;
+	LinkedList<Integer> adj[];
+	@SuppressWarnings("unchecked")
+	Graph(int v){
+		this.v=v;
+		adj=new LinkedList[v];
+		for(int i=0;i<v;i++)
+			adj[i]=new LinkedList<>();
+	}
+}
+class TopologicalSorting{
+	public static void addEdge(Graph g,int u,int v){
+		g.adj[u].add(v);
 	}
-
-	// 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)
+	public static void toposortutil(Graph g,int node,boolean visit[],Stack st)
 	{
-		// 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);
+		visit[node]=true;
+		int i;
+		Iterator<Integer>it=g.adj[node].iterator();
+		while(it.hasNext())
+		{
+			i=it.next();
+			System.out.println(i);
+			if(!visit[i])
+				toposortutil(g,i,visit,st);
 		}
-
-		// Push current vertex to stack
-		// which stores result
-		stack.push(new Integer(v));
+		System.out.println("node"+node);
+		st.push(node);
 	}
-
-	// 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() + " ");
+	public static void toposort(Graph g){
+		Stack st=new Stack();
+		boolean visit[]=new boolean[g.v];
+		for(int i=0;i<g.v;i++)
+			if(visit[i]==false)
+				toposortutil(g,i,visit,st);
+		while(st.empty()==false)
+			System.out.println(st.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();
+	public static void main(String[] args){
+		 Graph g = new Graph(6); 
+		TopologicalSorting tp=new TopologicalSorting();
+		tp.addEdge(g,5, 2); 
+        tp.addEdge(g,5, 0); 
+        tp.addEdge(g,4, 0); 
+        tp.addEdge(g,4, 1); 
+        tp.addEdge(g,2, 3); 
+        tp.addEdge(g,3, 1);
+		tp.toposort(g);
 	}
 }
-// This code is contributed by Aakash Hasija
+