// FixedPoints.java

// Written by Julian Devlin, 8/97, for the text book
// "Introduction to Probability," by Charles M. Grinstead & J. Laurie Snell

import java.applet.Applet;
import java.awt.*;

public class FixedPoints
	extends java.applet.Applet
{
	TextArea disp;		// Area to display HT
	
	Panel dispArea;
	Panel controls;		// Panel for user controls
	
	Label numl1;			// Controls
	TextField num1;
	Label numl2;			// Controls
	TextField num2;
	Button go;
	
	GridBagLayout gbl;
	GridBagConstraints cc;
	
	Combinatorics myC;
	String[] input;
		
	// Initialize applet
	public void init()
	{	
		numl1 = new Label("Number of permutations =");			// Create controls
		num1 = new TextField("100", 4);
		numl2 = new Label("Set size =");			// Create controls
		num2 = new TextField("20", 4);
		go = new Button("Go");
		
		disp = new TextArea(15, 20);		// Create display area
		
		dispArea = new Panel();				// Set up window
		controls = new Panel();
		setLayout(new BorderLayout(5, 5));
		
		add("South", controls);
		add("Center", dispArea);
		
		dispArea.setLayout(new GridLayout(1, 1));
		dispArea.add(disp);
		
		gbl = new GridBagLayout();
		controls.setLayout(gbl);
		
		cc = new GridBagConstraints();
		
		cc.gridx = 0;
		cc.gridy = 0;
		gbl.setConstraints(numl1, cc);
		controls.add(numl1);
		
		cc.gridx = 1;
		gbl.setConstraints(num1, cc);
		controls.add(num1);
		
		cc.gridx = 0;
		cc.gridy = 1;
		gbl.setConstraints(numl2, cc);
		controls.add(numl2);
		
		cc.gridx = 1;
		gbl.setConstraints(num2, cc);
		controls.add(num2);
		
		cc.gridx = 0;
		cc.gridy = 2;
		cc.gridwidth = 2;
		gbl.setConstraints(go, cc);
		controls.add(go);
		
		validate();
	}
	
	// Handle events
	public boolean handleEvent(Event evt)
	{
		if (evt.target instanceof Button)
		{
			if (evt.target == go && evt.id == Event.ACTION_EVENT)	// When button is clicked
			{
				disp.setText("");			// Reset output window
        		simulate(Integer.valueOf(num1.getText()).intValue(), 
        			Integer.valueOf(num2.getText()).intValue());
        		return true;					// Generate correct number of tosses
			}
		}
		return super.handleEvent(evt);	// Handle other events as usual
	}
	
	// Calculate probabilities
    public void simulate(int num, int size)
    {
    	String[] input = new String[size];
    	for (int i = 0; i < size; i++) {
    		input[i] = String.valueOf(i);
    	}
    	myC = new Combinatorics(input);
    	String[] results;
    	int[] fp = {0, 0, 0, 0, 0, 0};
    	int count;
    	int total = 0;
		for (int i = 0; i < num; i++) {
			count = 0;
	    	results = myC.randPerm();
	    	for (int j = 0; j < input.length; j++) {
	    		if (input[j] == results[j]) {
	    			count++;
	    			total++;
	    		}
	    	}
	    	if (count < 6)
	    		fp[count]++;
	    }
	    float prob[];
	    prob = new float[6];
	    for (int i = 0; i < 6; i++)
	    	prob[i] = (float) fp[i] / (float) num;
	    float avg;
	    avg = (float) total / (float) num;
	    
	    disp.appendText("Probability of fixed points:\n");
	    for (int i = 0; i < 6; i++) {
	    	disp.appendText(i + "    -    " + String.valueOf(prob[i]) + "\n");	
	    }
	    disp.appendText("\n\nAverage:    " + String.valueOf(avg) + "\n");
    }

}