60 lines
1.6 KiB
Java
60 lines
1.6 KiB
Java
package com.baeldung.prime;
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import java.util.Arrays;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.stream.Collectors;
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import java.util.stream.IntStream;
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public class PrimeGenerator {
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public static List<Integer> sieveOfEratosthenes(int n) {
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final boolean prime[] = new boolean[n + 1];
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Arrays.fill(prime, true);
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for (int p = 2; p * p <= n; p++) {
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if (prime[p]) {
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for (int i = p * 2; i <= n; i += p)
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prime[i] = false;
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}
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}
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final List<Integer> primes = new LinkedList<>();
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for (int i = 2; i <= n; i++) {
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if (prime[i])
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primes.add(i);
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}
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return primes;
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}
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public static List<Integer> primeNumbersBruteForce(int max) {
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final List<Integer> primeNumbers = new LinkedList<Integer>();
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for (int i = 2; i <= max; i++) {
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if (isPrimeBruteForce(i)) {
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primeNumbers.add(i);
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}
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}
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return primeNumbers;
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}
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private static boolean isPrimeBruteForce(int x) {
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for (int i = 2; i < x; i++) {
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if (x % i == 0) {
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return false;
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}
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}
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return true;
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}
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public static List<Integer> primeNumbersTill(int max) {
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return IntStream.rangeClosed(2, max)
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.filter(x -> isPrime(x))
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.boxed()
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.collect(Collectors.toList());
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}
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private static boolean isPrime(int x) {
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return IntStream.rangeClosed(2, (int) (Math.sqrt(x)))
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.allMatch(n -> x % n != 0);
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}
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}
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