Merge pull request #411 from jash-kothari/sieves-algo

Sieves Algorithm for prime number generation till n

Program's_Contributed_By_Contributors/Java_Programs/PrimeNumbers.java

@@ -0,0 +1,37 @@
+import java.util.*;
+import java.lang.*;
+import java.io.*;
+
+// Using the sieve of Eratosthenes
+public class PrimeNumbers {
+    public static List<Integer> calcPrimeNumbers(int n) {
+        boolean[] isPrimeNumber = new boolean[n + 1]; // boolean defaults to
+        // false
+        List<Integer> primes = new ArrayList<Integer>();
+        for (int i = 2; i < n; i++) {
+            isPrimeNumber[i] = true;
+        }
+        for (int i = 2; i < n; i++) {
+            if (isPrimeNumber[i]) {
+                primes.add(i);
+                // now mark the multiple of i as non-prime number
+                for (int j = i; j * i <= n; j++) {
+                    isPrimeNumber[i * j] = false;
+                }
+            }
+
+        }
+
+        return primes;
+    }
+
+    public static void main(String[] args) {
+        Scanner sc=new Scanner(System.in);
+        System.out.println("Enter the value of n");
+        int n=sc.nextInt();
+        List<Integer> calcPrimeNumbers = calcPrimeNumbers(n);
+        for (Integer integer : calcPrimeNumbers) {
+            System.out.println(integer);
+        }
+    }
+}