Primes.java

/**
 * Created by Connor on 10/19/15.
 */
public class Primes {
    /** class method called isPrime(int p) which determines if an integer p is a prime number. Assume p > 1. */
    public static boolean isPrime(int p) {
        if (p <= 1) return false;
        if (p == 2) return true;

        //check if n is a multiple of 2
        if (p%2==0) return false;
        //if not, check the odds
        for(int i = 3; i * i <= p; i += 2) {
            if( p % i == 0)
                return false;
        }
        return true;
    }

    /** method that prints out the first 100 prime numbers. */
    public static void printPrimes(){
        int numbersPrinted  = 0;
        int i = 0;
        while (numbersPrinted != 100){
            if (isPrime(i)){
                System.out.println(i);
                numbersPrinted++;
            }
            i++;
        }
    }

    /* method override for printPrimes() method that prints out the first n prime numbers. */
    public static void printPrimes(int n){
        int numbersPrinted  = 0;
        int i = 0;
        while (numbersPrinted < n){
            if (isPrime(i)){
                System.out.println(i);
                numbersPrinted++;
            }
            i++;
        }
    }

    /** method that returns how many prime numbers are less than or equal to the integer max. Note: max could be negative. */
    public static int countPrime(int max){
        int count = 0;

        if (max < 1) return 0;
        for (int i = 0; i <= max; i++) {
            if (isPrime(i)){
                count++;
            }
        }
        return count;
    }

    /** returns the sum of the first n prime numbers. */
    public static int sumPrime(int n) {
        if (n < 0) return 0;

        int sum = 0;
        int primeCount  = 0;
        int i = 0;
        while (primeCount < n){
            if (isPrime(i)){
                primeCount++;
                sum += i;
            }
            i++;
        }

        return sum;
    }

    /** returns the average of the first n prime numbers */
    public static double avePrime(int n){
        return (double) sumPrime(n) / n;

    }

    /** returns the maximum “distance” between each pair of consecutive prime numbers <= n. */
    public static int primeSpace(int n){
        int lastPrime = 0;
        int maxDistance = 0;
        int newDistance;
        for (int i = 0; i <= n; i++) {
            if (isPrime(i)){
                newDistance = (i - lastPrime);
                if (maxDistance < newDistance){
                    maxDistance = newDistance;
                }

                lastPrime = i;
            }

        }
        return maxDistance;

    }

    /** This method returns a String containing the prime factorization of the number n*/
    public static String factor(int n){
        int temp = n;
        String output = "";
        boolean found = false;
        if (!isPrime(n)) {
            while (temp != 1) {
                for (int primeNum = 2; !found; primeNum++) {
                    if (isPrime(primeNum)) {
                        if (temp % primeNum == 0) {
                            temp /= primeNum;
                            output += Integer.toString(primeNum) + "*";
                            found = true;
                        }
                    }

                }
                found = false;
            }
        }
        else if (n == 1) return output;
        else return Integer.toString(n);
        int length = output.length();

        //format output to not have '*' at the end
        return output.substring(0,length-1);

    }
}