Created
January 5, 2017 12:18
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Generating primes efficiently in java
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| import java.util.*; | |
| class finding_prime{ | |
| //For storing primes | |
| static ArrayList<Integer> primes = new ArrayList<>(); | |
| //Checking number is prime or not | |
| static boolean isPrime(Integer number){ | |
| //for itrating through primes list | |
| ListIterator theItretor = primes.listIterator(); | |
| //loop through list and and checking against all primes | |
| while(theItretor.hasNext()){ | |
| Object prime = theItretor.next(); | |
| if((number % Integer.parseInt(prime.toString())) == 0){ | |
| return false; | |
| } | |
| } | |
| return true; | |
| } | |
| //Main method | |
| public static void main(String[] args) { | |
| int maxCount = Integer.parseInt(args[0]);//No of primes no is needed | |
| /* | |
| Start finding prime number from 2 since 2 is first prime number and | |
| their is no prime number before that. | |
| */ | |
| for(int i = 2; i <= maxCount; i++){ | |
| //if(i is 2 ) add it to array since it is a prime | |
| if(i == 2){ | |
| primes.add(2); | |
| } | |
| //If not 2 then check is prime or not | |
| else if(isPrime(i)){ | |
| primes.add(i); | |
| } | |
| } | |
| System.out.println("Their are/is "+primes.size()+" primes here is the list"); | |
| System.out.println(); | |
| System.out.println(primes); | |
| } | |
| } |
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