prime number sieve added

Author: gkcs

src/main/java/main/java/videos/PrimeNumberSieve.java

@@ -0,0 +1,34 @@
+package main.java.videos;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class PrimeNumberSieve {
+
+ public static void main(String[] args) {
+ System.out.println(findAllPrimesUpto(100));
+ }
+
+ public static List<Integer> findAllPrimesUpto(final int n) {
+ final boolean[] touched = new boolean[n + 1];
+ final double sqrtOfN = Math.sqrt(n);
+ final List<Integer> primes = new ArrayList<>();
+ primes.add(2);
+ for (int i = 2; i < n; i += 2) {
+ touched[i] = true;
+ }
+ for (int i = 3; i <= sqrtOfN; i++) {
+ if (!touched[i]) {
+ for (int j = i * i; j <= n; j = j + (i * 2)) {
+ touched[j] = true;
+ }
+ }
+ }
+ for (int i = 2; i <= n; i++) {
+ if (!touched[i]) {
+ primes.add(i);
+ }
+ }
+ return primes;
+ }
+}