primesearch.java

javaP2P技术内幕课程111213141516源代码

package primecruncher;

import net.jxta.peergroup.PeerGroup;
import net.jxta.peergroup.PeerGroupFactory;
import net.jxta.exception.PeerGroupException;
import java.util.List;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Set;

/**
 * PrimeSearch finder. This program produces a list of prime numbers between 1 and a
 * given integer.
 */
public class PrimeSearch {

    public static int numPrimes(int from, int to) {
        return findPrimes(from, to).length;
    }

    public static int[] findPrimes(int from, int to) {


        if (from > to) {
            throw new IllegalArgumentException("First number must be smaller than the second.");
        }

       int[] list;

        //create an array containing all integers between the two specified numbers
        list = new int[to - from + 1];
        for (int i = 0; i < list.length; i++) {
            list[i] = from++;
        }

        //find out the module for each item in list, divided by each d, where
        //d is < or == to sqrt(to)
        //if the remainder is 0, the nubmer is a composite, and thus
        //we mark its position with 0 in the marks array,
        //otherwise the number is a prime, and thus mark it with 1
        //int maxDiv = (int)Math.sqrt(to);

        int maxDiv = (int)Math.sqrt(to);
        int[] mark = new int[list.length];
        for (int i=0; i < list.length; i++) {
            for (int z=2; z < maxDiv; z++) {
                if (list[i] != z && (list[i] % z == 0)) {
                    mark[i] = 1;
                }
            }
        }


        //create new array that contains only the primes, and return that array
        int primes = 0;
        for (int i=0; i < mark.length; i++) {
            if (mark[i] == 0) {
                primes++;
            }
        }
        int[] ret = new int[primes];
        int curs = 0;
        for (int i=0; i < mark.length; i++) {

            if (mark[i] == 0) {
                ret[curs] = list[i];
                curs++;
            }
        }

        return ret;



    }

}