1 /* 2 * Copyright (c) 2014 Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 package org.openjdk.bench.java.util.stream.tasks.PrimesFilter; 24 25 import java.util.ArrayList; 26 import java.util.List; 27 28 public class PrimesProblem { 29 30 /** 31 * Factors n into its prime factors. If n is prime, 32 * the result is a list of length 1 containing n. 33 * 34 * @param n the number to be factored 35 * @return a list of prime factors 36 */ 37 static List<Long> factor(long n) { 38 List<Long> flist = new ArrayList<>(); 39 40 while (n % 2L == 0) { 41 flist.add(2L); 42 n /= 2L; 43 } 44 45 long divisor = 3L; 46 while (n > 1L) { 47 long quotient = n / divisor; 48 if (n % divisor == 0) { 49 flist.add(divisor); 50 n = quotient; 51 } else if (quotient > divisor) { 52 divisor += 2L; 53 } else { 54 flist.add(n); 55 break; 56 } 57 } 58 59 return flist; 60 } 61 62 /** 63 * Tests whether n is prime. 64 * 65 * @param n the number to be tested 66 * @return true if n is prime, false if n is composite 67 */ 68 public static boolean isPrime(long n) { 69 List<Long> factors = factor(n); 70 return (factors.size() == 1); 71 } 72 73 74 }