previous Prime - Java java.lang

Java examples for java.lang:int prime

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Description

previous Prime

Demo Code



public class Main{
    public static long previousPrime(long input) {
        long lastFound = input;
        if (input == 2)
            return -1;
        else/*from   w  w  w.j a  va 2  s.c o  m*/
            lastFound -= 2;

        while (!PrimeUtil.isPrime(lastFound)) {
            lastFound -= 2;
        }
        return lastFound;
    }
    public static boolean isPrime(long num) {
        if (num < 2) {
            return false;
        } else if (num == 2) {
            return true;
        } else if (num % 2 == 0) {
            return false;
        } else {
            for (int divisor = 3; divisor <= Math.sqrt(num); divisor += 2) {
                if (num % divisor == 0) {
                    return false;
                }
            }
            return true;
        }
    }
}

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