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[MagmaMcFry]

Your version doesn't find largest prime factors larger than sqrt(n), since the algorithm stops before there. If you'd let it continue, it would take ages.

[Thief^]

You can make it go even faster by doing: (I would think)

Code: [Select]

@timed
def lpf2(n):  # had to modify a bit to accommodate Python
p = 2
if (p * p <= n):
while (n % p == 0):
n /= p
p += 1
while (p * p <= n):
if n % p == 0: n /= p
else: p += 2
return n

i.e. from 3 onwards stepping 2 at a time as prime numbers above 2 are always odd. If you unrolled it a bit more then after 3 you could step 2,2,4,2,4,2,4,2,4 to skip any multiples of 3, which would save a lot of redundant tests.

[Thief^]

Your version doesn't find largest prime factors larger than sqrt(n), since the algorithm stops before there. If you'd let it continue, it would take ages.

The way the 2nd algorithm works it has already removed all prime factors below sqrt(n) from n, so it's impossible for there to be any prime factors left above n except n itself.

[RulerOfNothing]

Your version doesn't find largest prime factors larger than sqrt(n), since the algorithm stops before there. If you'd let it continue, it would take ages.

The way the 2nd algorithm works it has already removed all prime factors below sqrt(n) from n, so it's impossible for there to be any prime factors left above n except n itself.

What happens if n is 202?

[Thief^]

It divides it by 2, then is left with 101. It then keeps going until it gets to 11, then calls 101 the highest prime factor.

[Mego]

I've written various algorithms over the past year or so for testing primality. I'll do some speed tests today after class, just because.

Also, anyone have any ideas about my Java problem?

[Dutchling]

Question: Is there a good reason to do this:

Code: [Select]

class Point:

    def __init__(self, initX, initY):
        self.x = initX
        self.y = initY

    def getX(self):
        return self.x

    def getY(self):
        return self.y

    def line_function(self,other):
        x_diff = other.x - self.x
        y_diff = other.y - self.y
        a = y_diff / x_diff
        b = self.y - a * self.x
        return (a,b,)

p = Point(0,17)
q = Point(5,27)

print(p.line_function(q))
instead of this:

Code: [Select]

class Point:

    def __init__(self, initX, initY):
        self.x = initX
        self.y = initY

    def getX(self):
        return self.x

    def getY(self):
        return self.y

def line_function(first,other):
        x_diff = other.x - first.x
        y_diff = other.y - first.y
        a = y_diff / x_diff
        b = first.y - a * first.x
        return (a,b,)

p = Point(0,17)
q = Point(5,27)

print(line_function(p,q))

[kaenneth]

Only if you also rename 'other' to 'second' =P

or if 'self' is a keyword in your language, like 'this' in C#

[Nadaka]

Yes, I'm aware of this. Working product before shiny product.

On another note, Java is baffling me.

Spoiler: GameButton.java (click to show/hide)

Code: [Select]

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;

public class GameButton extends JButton implements MouseListener {
    GameGUI gameg;
    GamePieces color;
   
    public GameButton(String imgFile, GameGUI gguiInstance) throws IOException {
        super(new ImageIcon(imgFile));
        gameg = gguiInstance;
        if(imgFile.equals("black.png")) color = GamePieces.BLACK;
        else if(imgFile.equals("white.png")) color = GamePieces.WHITE;
        else color = GamePieces.EMPTY;
this.addMouseListener(this);
    }
   
    public void mouseClicked(MouseEvent e) {
        if(e.getButton() == MouseEvent.BUTTON1) gameg.processClick(this);
        System.out.println("GameButton " + this.toString() + " pressed.");
    }

public void mouseEntered(MouseEvent e) {
        //nothing to see here, move along
    }

public void mouseExited(MouseEvent e) {
        //nothing to see here, move along
    }

public void mousePressed(MouseEvent e) {
        //nothing to see here, move along
    }

public void mouseReleased(MouseEvent e) {
        //nothing to see here, move along
    }
   
    public int getXPos() {
        return (int)super.getX()/100;
    }
   
    public int getYPos() {
        return (int)super.getY()/100;
    }
   
    public GamePieces getColor() {
        return this.color;
    }
}


Spoiler: GameGUI.java (click to show/hide)

Code: [Select]

import javax.swing.*;
import java.awt.*;
import java.io.*;

public class GameGUI {
    JFrame frame;
   
    public GameGUI(JFrame frame) {
        this.frame = frame;
    }
   
    public void processClick(GameButton gb) {
        String fileName;
        if(gb.getColor() == GamePieces.BLACK || gb.getColor() == GamePieces.EMPTY) fileName = "white.png";
        else fileName = "black.png";
        frame.remove(gb);
        try {
            gb = new GameButton(fileName, this);
        } catch(IOException e) {
            return;
        }
        frame.getContentPane().add(gb);
        frame.pack();
        frame.setVisible(true);
    }
   
}


Spoiler: GamePieces.java (click to show/hide)

Code: [Select]

public enum GamePieces
{
    EMPTY, BLACK, WHITE;
}


Spoiler: GUITest.java (click to show/hide)

Code: [Select]

import java.io.IOException;
import javax.swing.*;
import java.awt.*;

public class GUITest {
    public static void main(String[] args) throws IOException {
        JFrame testFrame = new JFrame("Game Window (debug)");
        GameGUI gg = new GameGUI(testFrame);
       
        testFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        testFrame.getContentPane().add(new GameButton("black.png", gg));
        testFrame.pack();
        testFrame.setVisible(true);
    }
}


Everything appears to work fine. The window appears with a button in it, which has the icon represented by black.png. Except, when I try to click it, nothing happens. The various debugging things I put in GameButton.mouseClicked and GameGUI.processClick aren't doing anything. Where am I going wrong?

You have nothing tying the button to the method you want to call. I see you have a mouseClicked(MouseEvent e) method on your button class. If you don't implement the MouseListener interface, that is meaningless. You also have to bind the button object to an instance of the MouseListener. If your GameButton class implements the  interface MouseListener, the button can be its own MouseListener, and you can bind itself to itself in its constructor. I have modified the code of your GameButton class for this. Note that you could alternatively used an ActionListener.

AKA: Yo dog, I heard you like to MouseListen, so I put a MouseListener in your MouseListener, so you can MouseListen while you MouseListen.

[Mego]

Yes, I'm aware of this. Working product before shiny product.

On another note, Java is baffling me.

Spoiler: GameButton.java (click to show/hide)

Code: [Select]

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;

public class GameButton extends JButton implements MouseListener {
    GameGUI gameg;
    GamePieces color;
   
    public GameButton(String imgFile, GameGUI gguiInstance) throws IOException {
        super(new ImageIcon(imgFile));
        gameg = gguiInstance;
        if(imgFile.equals("black.png")) color = GamePieces.BLACK;
        else if(imgFile.equals("white.png")) color = GamePieces.WHITE;
        else color = GamePieces.EMPTY;
this.addMouseListener(this);
    }
   
    public void mouseClicked(MouseEvent e) {
        if(e.getButton() == MouseEvent.BUTTON1) gameg.processClick(this);
        System.out.println("GameButton " + this.toString() + " pressed.");
    }

public void mouseEntered(MouseEvent e) {
        //nothing to see here, move along
    }

public void mouseExited(MouseEvent e) {
        //nothing to see here, move along
    }

public void mousePressed(MouseEvent e) {
        //nothing to see here, move along
    }

public void mouseReleased(MouseEvent e) {
        //nothing to see here, move along
    }
   
    public int getXPos() {
        return (int)super.getX()/100;
    }
   
    public int getYPos() {
        return (int)super.getY()/100;
    }
   
    public GamePieces getColor() {
        return this.color;
    }
}


Spoiler: GameGUI.java (click to show/hide)

Code: [Select]

import javax.swing.*;
import java.awt.*;
import java.io.*;

public class GameGUI {
    JFrame frame;
   
    public GameGUI(JFrame frame) {
        this.frame = frame;
    }
   
    public void processClick(GameButton gb) {
        String fileName;
        if(gb.getColor() == GamePieces.BLACK || gb.getColor() == GamePieces.EMPTY) fileName = "white.png";
        else fileName = "black.png";
        frame.remove(gb);
        try {
            gb = new GameButton(fileName, this);
        } catch(IOException e) {
            return;
        }
        frame.getContentPane().add(gb);
        frame.pack();
        frame.setVisible(true);
    }
   
}


Spoiler: GamePieces.java (click to show/hide)

Code: [Select]

public enum GamePieces
{
    EMPTY, BLACK, WHITE;
}


Spoiler: GUITest.java (click to show/hide)

Code: [Select]

import java.io.IOException;
import javax.swing.*;
import java.awt.*;

public class GUITest {
    public static void main(String[] args) throws IOException {
        JFrame testFrame = new JFrame("Game Window (debug)");
        GameGUI gg = new GameGUI(testFrame);
       
        testFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        testFrame.getContentPane().add(new GameButton("black.png", gg));
        testFrame.pack();
        testFrame.setVisible(true);
    }
}


Everything appears to work fine. The window appears with a button in it, which has the icon represented by black.png. Except, when I try to click it, nothing happens. The various debugging things I put in GameButton.mouseClicked and GameGUI.processClick aren't doing anything. Where am I going wrong?

You have nothing tying the button to the method you want to call. I see you have a mouseClicked(MouseEvent e) method on your button class. If you don't implement the MouseListener interface, that is meaningless. You also have to bind the button object to an instance of the MouseListener. If your GameButton class implements the  interface MouseListener, the button can be its own MouseListener, and you can bind itself to itself in its constructor. I have modified the code of your GameButton class for this. Note that you could alternatively used an ActionListener.

AKA: Yo dog, I heard you like to MouseListen, so I put a MouseListener in your MouseListener, so you can MouseListen while you MouseListen.

Ahh, the issue is that I forgot to call addMouseListener. Implementing MouseListener is unnecessary, because JButton already does it.

I'm eating my words now. Disregard that bit, silly casting.

[LoSboccacc]

If you need just click, why don't you add an actionlistener?

That's fairly reliable. And also help doubleclicks.

[MagmaMcFry]

Your version doesn't find largest prime factors larger than sqrt(n), since the algorithm stops before there. If you'd let it continue, it would take ages.

The way the 2nd algorithm works it has already removed all prime factors below sqrt(n) from n, so it's impossible for there to be any prime factors left above n except n itself.

I'm talking about the first algorithm. You'll notice that I wrote the second one myself.

[SethCreiyd]

Your version doesn't find largest prime factors larger than sqrt(n), since the algorithm stops before there. If you'd let it continue, it would take ages.

The way the 2nd algorithm works it has already removed all prime factors below sqrt(n) from n, so it's impossible for there to be any prime factors left above n except n itself.

I'm talking about the first algorithm. You'll notice that I wrote the second one myself.

Yeah, I certainly have a lot to learn and practice:

Spoiler (click to show/hide)

My solution to a problem:

Code: [Select]

    min = None
    i = 0
    while not min:
        i += 20
        for x in xrange(3, 20, 1):
            if i % x != 0:
                break
        else:
            min = i
    return min
Appallingly cumbersome, naturally, feels like using a battering ram to get into the broom closet.
There are many other answers like that posted there, but then there was this:

Code: [Select]

def gcd(x, y):
    while x % y != 0:
        x, y = y, x % y
    return y
   
def lcm(x, y):
    return x * y / gcd(x, y)
   
print reduce(lcm, xrange(2, 21))

Which takes about 30 ms, and is another reminder of what a novice I am.  Using LCM or reduce* didn't even cross my mind.  I hope feeling dumb is part of the process of learning to apply math correctly and not to brute-force everything.

_{*"Apply function of two arguments cumulatively to the items of iterable, from left to right, so as to reduce the iterable to a single value."}

[LoSboccacc]

There is even another step, not using math at all because you can just copy a solution from the web

[SethCreiyd]

There's that, but I'd like to be able to produce more clever solutions to problems rather than learning about them afterward or having someone else do the thinking, and even so, the site whose problems I'm working on discourages copypasta:

Q. I solved it by using a search engine, does that matter?

A. Making use of the internet to research a problem is to be encouraged as there could be hidden treasures of mathematics to be discovered beneath the surface of many of these problems. However, there is a fine line between researching ideas and using the answer you found on another website. If you photocopy a crossword solution then what have you achieved?

And you can't see other people's solutions for a problem there, until you answer it correctly.  The reduce(lcm, xrange(2, 21)) solution is just so much better than mine that I wish I'd thought of it.