Sieve of eratosthenes

Author: siddhant2002

Programs/Sieve_Of_Eratosthenes.java

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+// Program to find all the primes upto N using Sieve Of Eratosthenes technique.
+// A number is called prime if it has only two factors (1 and the number itself)
+import java.util.*;
+public class Sieve_Of_Eratosthenes
+{
+    public static void main(String args[])
+    {
+        Scanner sc=new Scanner(System.in);
+        Sieve_Of_Eratosthenes nm=new Sieve_Of_Eratosthenes();
+        int n=sc.nextInt();
+        // input taken upto which primes which will be displayed
+        boolean k[]=nm.sieve_Of_Eratosthenes(n);
+        // method calling where an integer value is sent and a boolean array is stored as a return value
+        for(int i=0;i<=20000000;i++)
+        {
+            if(k[i])
+            {
+                System.out.print(i+" ");
+            }
+        }
+        System.out.println();
+    }
+    boolean[] sieve_Of_Eratosthenes(int n)
+    {
+        boolean b[]=new boolean[n+1];
+        // boolean array is created 
+        Arrays.fill(b,true);
+        b[0]=false;
+        b[1]=false;
+        // 0 & 1 are marked as false because they are neither prime nor composite
+        for(int i=2;i<=Math.sqrt(n);i++)
+        {
+            // loop is started from 2
+            if(b[i])
+            {
+                for(int j=i*i;j<=n;j+=i)
+                {
+                    // every multiple of the ith value is marked as false because they have a factor i
+                    b[j]=false;
+                }
+            }
+        }
+        return b;
+        // boolean array is returned
+    }
+}