//RandomWalk2.java
//avoid re-visiting a point

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

public class RandomWalk2 extends JApplet {
    
    int lines;
    int scale;   //conversion to screen pixels

    public void init() {
	String input;
	
	input = JOptionPane.showInputDialog("Enter # of steps to take");
	lines = Integer.parseInt(input);

	input = JOptionPane.showInputDialog("Enter scale factor");
	scale = Integer.parseInt(input);
    }
    
    public void paint( Graphics g ) {
	super.paint( g );

	int xPrev, yPrev, xNow, yNow;
	int xCenter=getWidth()/2;
	int yCenter=getHeight()/2;
	double totalDist=0, avgDist=0, dist;
	//int scale=15;   //conversion to screen pixels
	int [] X = new int[lines+1];   //**
	int [] Y = new int[lines+1];
	boolean foundNew;
	int attempts;

	xPrev = xNow = xCenter;   //start in center
	yPrev = yNow = yCenter;
	X[0] = xNow;     //**
	Y[0] = yNow;
	g.setColor(Color.RED);
	g.fillRect(xPrev-3,yPrev-3,5,5);
	g.setColor(Color.BLACK);       

	for (int step=1; step<=lines; step++) {
	    foundNew = false;  //**
	    attempts = 0;
	    do {
		switch ((int)(Math.random()*4)) {
		case 0:  //up
		    yNow = yPrev - scale;
		    break;
		case 1:  //down
		    yNow = yPrev + scale;
		    break;
		case 2:  //left
		    xNow = xPrev - scale;
		    break;
		case 3:  //left
		    xNow = xPrev + scale;
		    break;
		}
		if (!pairExists(X,Y,xNow,yNow,step))   //**
		    foundNew = true;
	    } while (!foundNew && ++attempts<30);   //**avoid inf. loop if stuck

	    
	    if (attempts == 30)   //**indicates was probably stuck
		//should check each 8 nbors to see if any unvisited yet...
		g.setColor(Color.RED);
	    else
		g.setColor(Color.BLACK);

	    g.drawLine(xPrev,yPrev,xNow,yNow);
	    
	    X[step] = xNow;     //**
	    Y[step] = yNow;
	    xPrev = xNow;
	    yPrev = yNow;
	    
	    int x = (xNow - xCenter) / scale;
	    int y = (yNow - yCenter) / scale;
	    dist = Math.sqrt(x*x+y*y);
	    totalDist += dist;
	    avgDist = totalDist / step;
	    
	    showStatus("Distance from origin: " + (int)dist + 
		       "   Average distance: " + (int)avgDist);

	}
    }

    //**
    public boolean pairExists(int[] A, int[] B, int x, int y, int numPoints) {
	int i=0;
	while (i<numPoints && (A[i]!=x || B[i]!=y))
	    i++;
	if (i<numPoints)
	    return true;
	else
	    return false;
    }
}
/*change scale for zoom
add ending point as blue rectangle
input scale factor from user
add Thread.sleep
input sleep value from user
*/