Usage Of Sieve Of Eratosthenes For Finding Primes Faster
Jun 27, 2014
I found this method from the same link from which I found the Pandigital method. This method uses the algorithm of sieve of eratosthenes who was a greek mathematician and showed how to find prime numbers by taking an individual number and finding the multiples of it and cut them out for they will not be a prime number. From what I've seen this program gives the results much faster than the traditional way of searching for prime numbers by diving that number by the digits upto half of that number and check for divisiblity.
Well, here's the code
public int[] ESieve(int upperLimit) {
int sieveBound = (int)(upperLimit - 1) / 2;
int upperSqrt = ((int)Math.Sqrt(upperLimit) - 1) / 2;
BitArray PrimeBits = new BitArray(sieveBound + 1, true);
for (int i = 1; i <= upperSqrt; i++) {
if (PrimeBits.Get(i)) {
[Code] .....
As seen from the full program on the site [URL] .... this program was formely writen in C++ and from there I've scrapped out this method as the syntax are corresponding to that of Java, but one problem I faced was in finding the BitArray class in Java. I was unable to understand the approach of this program to find the prime numbers.
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Feb 9, 2015
I am trying to figure out the Sieve of Eratosthenes program using arrays. I am trying to display the prime numbers of 1-100. My code right now is:
import java.text.DecimalFormat;
import java.util.Scanner;
public class TextLab06st
{
public static void main(String args[])
{
// This main method needs additions for the 100 point version.
Scanner input = new Scanner(System.in);
System.out.println("
TextLab06
[code]...
I am getting the error <identifier? expected for the line "primes.[index] = false;"
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Jan 11, 2014
Java Code:
class Program {
public static void main (String[] args) {
long max = 200; //add up all primes up to 200
long ans = 0;
for(long x = 2; x < max; x++) {
if(isPrime(x)) {
ans += x;
[Code] ....
This code adds up all of the primes before a certain number (max). Unfortunately, it is much too slow when you get up to bigger numbers - how can I do this more efficiently.
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Apr 12, 2014
obstacleX = (int) (obstacleX - 0.1);
if(obstacleX <= 0){
obstacleX = 600;
}
repaint();
Thats my code, and the rectangle (ObstacleX is the X cordinate for the rectangle) goes fine on the first few times across the screen, then starts to go hyperspeed....
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Feb 5, 2014
I am working on a problem that computes primes. Here is the problem: You are going to implement a class that computes all the primes up to some integer n. The technique you are to use was developed by a Greek named Eratosthenes who lived in the third century BC. The technique is known as the Sieve of Eratosthenes. The algorithm is described by the following pseudocode:
create a queue and fill it with the consecutive integers 2 through n inclusive.
create an empty queue to store primes.
do {
obtain the next prime p by removing the first value in the queue of numbers.
put p into the queue of primes.
go through the queue of numbers, eliminating numbers divisible by p.
} while (p < sqrt(n))
all remaining values in numbers queue are prime, so transfer them to primes queue
You are to use the Queue interface provided. When you want to construct a Queue object, you should make it of type LinkedQueue. These classes are included. You should define a class called Sieve with the following public methods:
Sieve() - Constructs a sieve object.
void computeTo(int n) - This is the method that should implement the sieve algorithm. All prime computations must be implemented using this algorithm. The method should compute all primes up to and including n. It should throw an IllegalArgumentException if n is less than 2.
void reportResults() - This method should report the primes to System.out. It should throw an IllegalStateException if no legal call has been made yet on the computeTo method. It is okay for it to have an extra space at the end of each line.
int getMax() - This is a convenience method that will let the client find out the value of n that was used the last time computeTo was called. It should throw an IllegalStateException if no legal call has been made yet on the computeTo method.
int getCount() - This method should return the number of primes that were found on the last call on computeTo. It should throw an IllegalStateException if no legal call has been made yet on the computeTo method.
Your reportResults method should print the maximum n used and should then show a list of the primes, 12 per line with a space after each prime. Notice that there is no guarantee that the number of primes will be a multiple of 12. The calls on reportResults must exactly reproduce the format of the sample log. The final line of output that appears in the log reporting the percentage of primes is generated by the main program, not by the call on reportResults.
Here is my class Sieve. I am having difficulty getting all the primes into the proper queue:
public class Sieve {
private Queue<Integer> primes;
private Queue<Integer> numList;
private boolean computed = false;
private int max;
private int count = 0;
[Code] ....
When I input say, 20, I only get 2, 3, and 11 back as primes. Somewhere in the algorithm (lines 40-54) I seem to have gone awry, but I'm not certain where. Here are the other classes:
SieveMain:
// This program computes all the prime numbers up to a given integer n. It uses the classic "Sieve of Eratosthenes" to do so.
import java.util.*;
public class SieveMain {
public static void main(String[] args) {
System.out.println("This program computes all prime numbers up to a");
System.out.println("maximum using the Sieve of Eratosthenes.");
System.out.println();
[Code] .....
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Jan 31, 2014
I don't know if this is appropriate to Swing/AWT, or even if this is a Java issue, but I had quite a shock recently. I have been working on a kind of drawing program in which the user can select tiny control rectangles and drag them around, causing the shape of a polygon to change. (They are not implemented as Java Polygons or Shapes because some are one-dimensional). I have gotten it into pretty good shape, so I exported it from Eclipse, my development platform, into a standalone Java application. In the standalone application, each time I drag the mouse, the redrawing shows nasty flickering, as if it's running too slowly. While I was developing the application inside Eclipse, it ran perfectly, with no flickering whatsoever.
What gives? I'd expect that the in-Eclipse runs would be slower, because they're burdened with extra debugging baggage, while the exported standalone version should run faster. But the reverse is the case.
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Apr 1, 2015
When I compile the code, it goes through fine in the compiler. However after entering the boundaries for the lower an upper it doesn't produce the prime pairs between the two boundaries that the user sets. I have tried changing some of my integers that i initialized no luck. I looked at the last section of public void showPrimes() . However I can't seem to see where it has gone wrong there. I have included the entire code, plus the section again that I think is wrong. I have also posted the final output of what it looks like and what else should be included to make it easier to see what I am missing. Basically it keeps giving me zero primes even when the boundary is 100 and 200, or so and so forth.
import java.util.Scanner;
public class kbeaudry_xSieve
{
public static void main (String args[]){
kbeaudry_xSieve i = new kbeaudry_xSieve();
}
boolean primes[] = new boolean [50001];
int upper;
int lower;
[code]....
This is what i get when I actually run the program. However in the section where I have added *****, this is where it should put the prime pairs in.
Please enter a lower boundary and an upper boundary and I will print all of the sexy prime pairs between those boundaries.
Please enter the lower boundary (between 1 and 50000): 200
Please enter the upper boundary (between 1 and 50000): 600
There were 0 sexy pairs displayed between 200 and 600.. I am still working on another code for my that I had issues with, however I had to go out of the country for a few days to take care of some work.
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Jan 16, 2015
I am doing a sieve code to find prime numbers.
public static void main(String[] args)
{
Scanner scanner = new Scanner(System.in);
System.out.println(" Enter the maximum number ");
int maxNumber = scanner.nextInt();
int[]numberList = createList (maxNumber);
[code]....
I have a problem with the output. It only get as far as marking the multiples of 2. It does not mark the multiples of 3 and so on.Example output: If the range is from 2 to 15 the output is :2, 3, 0, 5, 0, 7, 0, 9, 0, 11, 0, 13, 0, 15 note: 0 means its marked.As you can see it only marks multiples of 2 but it does not mark multiples of 3 above. I think the problem lies in the for loop inside my main method, because the index does not increment.
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My template code is:
Java Code: public class GetCPUUsage{
public static void main(String[] args){
System.out.println("CPU USAGE IS: ??????");
}
} mh_sh_highlight_all('java');
I added ??? as placeholder for CPU usage because I do not know how to retrieve RAM usage by Java.
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//concrete implementation
return query;
}
}
I have another class Command2. Here I need a similar method. The only difference is in the type of parameters passed. (type String and type Command).
public class Command2 {
//TO DO:
public StringBuffer addFilter(String query, Command2 cmd) {
//concrete implementation
return query;
}
}
I have started by using Interface
public interface Helper {
public StringBuffer addFilter(String query, XXXXX parameter2);
}
I would like the classes Command1 and Command2 to implement the interface Helper and override it these two public classes.
However my problem is in dealing with the 2nd parameter. Am I right in my approach? How do I handle this issue?
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The Server, as seen below, has two threads. I explain what the threads do before the code. There is also another while loop running constantly in the server that is waiting for sockets to connect. The loop does not run constantly at the line socket.accept(); it stops and just waits.
The User, split into a menu and chat window, has two threads as well. I explain what the threads do before the code. After I originally posted I put a 100 ms sleep in all my threads. CPU Usage is still at 100%*
This thread listens for input from the user. The input tells the server what action to take. There is a thread running for every user currently connected to the server.
public void run()
{
try
{
input = new DataInputStream(user.getSocket().getInputStream());
output = new DataOutputStream(user.getSocket().getOutputStream());
[code]....
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import java.io.OutputStream;
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[Code]....
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Declaring the method as static precludes one from using any sort of object oriented programming, thus the method cannot access instance fields of the object if it needs to.
I created two short classes to sort of find out what this meant, but I feel I do not understand it well enough.
Test class (main):
package votek;
public class Test {
public static void main(String[] args) {
SomeMethod();
}
public static void SomeMethod() {
Character character = new Character();
character.totalLevel = 50;
System.out.println(character.totalLevel);
}
}
Character class:
package votek;
public class Character {
private int level = 0;
public Character() {
level = 50;
}
}
OR
Does it mean that making a static method in the class with private instances will prevent the method from using the private instances?
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[code]....
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int Findit = numbers[0][0];
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[Code] ....
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[Code] .....
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Scanner input = new Scanner(System.in);
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[code]....
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[code]....
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