## Monday, 26 December 2016

### Chapter 15 Exercise 34, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

15.34 (Simulation: self-avoiding random walk)
A self-avoiding walk in a lattice is a path from one point to another
that does not visit the same point twice. Self- avoiding walks have applications
in physics, chemistry, and mathematics. They can be used to model chain-like
entities such as solvents and polymers. Write a program that displays a random
path that starts from the center and ends at a point on the boundary, as shown
in Figure 15.37a or ends at a dead-end point (i.e., surrounded by four points that
have already been visited), as shown in Figure 15.37b. Assume the size of the lattice
is 16 by 16.

import javafx.collections.ObservableList;
import javafx.geometry.Point2D;
import javafx.scene.Node;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Line;
import javafx.scene.text.Text;

import java.util.ArrayList;

public class PaneCollection {

public static void drawArrowLine(double x1, double y1, double x2,   double y2, Pane pane) {
drawArrowLine(x1, y1, x2, y2, pane, 15);
}

public static void drawArrowLine(double x1, double y1, double x2,   double y2, Pane pane, int length) {
drawArrowLine(new Line(x1, y1, x2, y2), pane, length);
}

public static void drawArrowLine(Line line, Pane pane) {
drawArrowLine(line, pane, 15);
}

public static void drawArrowLine(Line line, Pane pane, int length) {
ObservableList<Node> list = pane.getChildren();

double arctan = Math.atan(slope(line));
double set45 = (line.getStartX() > line.getEndX()) ? 1.57 / 2 : -1.57 * 1.5;

(line.getEndX() + Math.cos(arctan - set45) * length),
(line.getEndY() + Math.sin(arctan - set45) * length)));
(line.getEndX() + Math.cos(arctan + set45) * length),
(line.getEndY() + Math.sin(arctan + set45) * length)));
}

public static double slope(Line line) {
return (line.getStartY() - line.getEndY()) / (line.getStartX() - line.getEndX());
}

public static double distance(double x1, double y1, double x2, double y2) {

return Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
}

public static double distance(Line line) {
return distance(line.getStartX(), line.getStartY(), line.getEndX(), line.getEndY());
}

public static MyPoint getCenterPoint(Line line) {

return new MyPoint(
(line.getStartX() + line.getEndX()) / 2,
(line.getStartY() + line.getEndY()) / 2);
}

public static void drawPointCounter(Pane pane, Point2D[] points) {
int counter = 1;

for (Point2D point : points) {
Circle temp = new Circle(point.getX(), point.getY(), 5, Color.TRANSPARENT);
Text text = new Text(point.getX(), point.getY(), "" + counter++);
}
}

public static boolean containsPoint(ArrayList<Point2D> points, double x, double y) {
for (Point2D p : points) {
if (p.getX() == x && p.getY() == y) return true;
}
return false;
}

public static boolean removePoint(ArrayList<Point2D> points, double x, double y) {

int index = 0;
for (Point2D p : points) {
if (p.getX() == x && p.getY() == y) {
points.remove(index);
return true;
}
index++;
}
return false;
}

public static Line copyLine(Line l) {
return new Line(l.getStartX(), l.getStartY(), l.getEndX(), l.getEndY());
}

}


import javafx.application.Application;
import javafx.geometry.Point2D;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Line;
import javafx.stage.Stage;

import java.util.ArrayList;

public class Exercise_34 extends Application {

@Override
public void start(Stage primaryStage) throws Exception {

RandomWalkPane pane = new RandomWalkPane();

primaryStage.setScene(new Scene(pane));
primaryStage.setTitle("Random Walk");
primaryStage.show();
}

public static void main(String[] args) {
Application.launch(args);

}

private class RandomWalkPane extends Pane {

private double size = 20;
private double squareCount = 16;
private double w = size * squareCount;
private double h = w;
private Point2D centerP = new Point2D(w / 2, h / 2);
private Point2D currentP = centerP;

private boolean hasHitBorder;

// All valid points
ArrayList<Point2D> points = new ArrayList<>();
// Line Path
//ArrayList<Line> lines = new ArrayList<>();

private RandomWalkPane() {

setPrefWidth(w);
setPrefHeight(h);

drawLayout();

while (nextPath() && !hasHitBorder);
}

private void drawLayout() {

// horizontal lines and adding possible points to array
for (int i = 0; i <= squareCount; i++) {
Line line = new Line(0, i * size, w, i * size);
line.setOpacity(0.1);

for (int j = 0; j <= squareCount; j++) {
double x = j * size;
double y = i * size;

}
}

// since we start at the center
// remove center point from points
PaneCollection.removePoint(points, centerP.getX(), centerP.getY());

// vertical line
for (int i = 0; i < squareCount; i++) {
Line line = new Line(i * size, 0, i * size, h);
line.setOpacity(0.1);
}
}

private boolean nextPath() {
// get possible paths
Point2D[] possiblePs = new Point2D[4];
possiblePs[0] = new Point2D(currentP.getX(), currentP.getY() - size); // up
possiblePs[1] = new Point2D(currentP.getX(), currentP.getY() + size); // down
possiblePs[2] = new Point2D(currentP.getX() - size, currentP.getY()); // left
possiblePs[3] = new Point2D(currentP.getX() + size, currentP.getY()); // right

boolean hasMoved = false;
boolean[] isUsed = new boolean[possiblePs.length];

for (int i = 0; i < 4;) {
int ranIndex = (int) (Math.random() * 4);

if (!isUsed[ranIndex]) {
isUsed[ranIndex] = true;
i++;
Point2D p = possiblePs[ranIndex];
if (PaneCollection.containsPoint(points, p.getX(), p.getY())) {

// draw path
Line line = new Line(
currentP.getX(), currentP.getY(),
p.getX(), p.getY());
currentP = p; // update current Point

// remove point from point tracker
PaneCollection.removePoint(points, p.getX(), p.getY());

// make the new point the current point
// update hasMoved
hasMoved = true;
checkBorder(currentP);

break; // break out of loop early
}

}
}

return hasMoved; // return moved status
}

private void checkBorder(Point2D p) {
double x = p.getX();
double y = p.getY();

if (x <= 0 || x >= w) hasHitBorder = true;
if (y <= 0  || y >= h) hasHitBorder = true;
}
}
}