Java examples for java.lang:int prime
Generate Unique prime Factors
//package com.java2s; import java.util.Set; import java.util.TreeSet; public class Main { /**// ww w .j a v a 2 s. c om * Generate Unique primeFactors * * @param num * @return empty if no is prime. */ public static Set<Integer> primeFactors(int num) { Set<Integer> t = new TreeSet<Integer>(); if (num < 2) { // t.add(2); return t; } for (int i = 2; i <= Math.sqrt(num); i++) { if (chkPrime(i)) { if (num % i == 0) { t.add(i); if ((i != num / i) && chkPrime(num / i)) t.add(num / i); else t.addAll(primeFactors(num / i)); } } } return t; } /** * Deterministic Prime testing. * * @param num * @return */ public static boolean chkPrime(int num) { if (num == 1) return false; if (num == 2 || num == 3) return true; if (num % 2 == 0) return false; else if (num % 3 == 0) return false; for (int i = 5; i * i <= num; i += 2) { if (num % i == 0) return false; } return true; } }