Develop Reference

Robot race -> robot moves on cartesian grid. L is Left 90 degrees, R is right 90 degrees and F is forward one space. Please see attached screenshot

Click here to see the questionRobot Race
How can I make multiple robots run simultaneously. I have created run method that keeps track of x and y co-ordinates for each action
import java.util.LinkedList;
import java.util.Queue;
public class Robot implements Runnable {
private int delay;
private String actions;
private String name;
int x = 0;
int y = 0;
// 2d array for 4 direction on cartesian grid
int[][] move = {{0,1}, {1,0}, {-1,0}, {0,-1}};
int dir = 0;
int time = 1;
Queue<Character> queue = new LinkedList<>();
public Robot(int delay, String actions, String name) {
this.delay = delay;
this.actions = actions;
this.name = name;
}
#Override
public void run() {
for (char ch: actions.toCharArray()) {
if (ch == 'F') {
x += move[dir][0];
y += move[dir][1];
} else if (ch == 'L') {
dir++;
} else if (ch == 'R') {
dir--;
}
// to avoid overflow
dir = (dir + 4) % 4;
System.out.println(time+ "s " +name+ ": Moves " +ch);
time++;
try {
Thread.sleep(delay * 1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
new Robot(3, "FFFLRFRLFF", "Joe").run();
new Robot(1, "FFFFFLF", "Bill").run();
}
}
`

How can I make multiple robots run simultaneously.
You need to start a separate Thread for each Robot.
The reason your class implements Runnable is so it can be used as a Thread.
So to start a Thread for each Robot the basic code would be:
//new Robot(3, "FFFLRFRLFF", "Joe").run();
Robot robot1 = new Robot(3, "FFFLRFRLFF", "Joe")
new Thread(robot1).start();
When the Thread starts it will invoke the run() method.

Greenfoot - isKeyDown() seems to hold its value

This is a sprinting function for a game, if the player has greater then 0% spring left then he can sprint, if it is at 0% the player cannot sprint. If the player is not sprinting then the sprint % will start to regenerate.
The problem:
When the player hits 0% sprint the player is still able to sprint.
public class User extends Characters
{
private int walk = 3;
private int run = 10;
private int speed = walk;
private boolean isRunning = false;
private int runDuration = 100;
private int baseRunDuration = 100;
private int runCoolDown = 300;
public void act()
{
playerMove();
}
//Contains movement inputs as well as run imputs
void playerMove(){
getWorld().showText("Run Duration: " + runDuration, 100, 100);
if(Greenfoot.isKeyDown("w") ){
setLocation(getX(), getY()-speed);
}
if(Greenfoot.isKeyDown("a")){
move(-speed);
}
if(Greenfoot.isKeyDown("s")){
setLocation(getX(), getY()+speed);
}
if(Greenfoot.isKeyDown("d")){
move(+speed);
}
if(Greenfoot.isKeyDown("shift") && runDuration > 0){
if(runDuration > 0){
isRunning = true;
speed = run;
runDuration--;
}
}
else{
speed = walk;
isRunning = false;
}
if(isRunning == false){
if(runDuration < baseRunDuration){
runDuration++;
}
}
}
}

Obicere is right that you are either sprinting, or you're alternately sprinting and not sprinting, giving a half-speed sprint. There's various ways to fix this. I'd suggest only recharging your sprint when you're not moving. You can do this using a boolean to keep track of whether you've moved this frame, or simply by using else-if to change your middle block of code to:
if(Greenfoot.isKeyDown("w") ){
setLocation(getX(), getY()-speed);
}
else if(Greenfoot.isKeyDown("a")){
move(-speed);
}
else if(Greenfoot.isKeyDown("s")){
setLocation(getX(), getY()+speed);
}
else if(Greenfoot.isKeyDown("d")){
move(+speed);
}
else if(runDuration < baseRunDuration){
runDuration++;
}
Note the new elses, and the final clause on the end which is moved up from the bottom of your code.

Make an image change on hero direction, Simple 2D game

Hi every one i am having a bit of trouble with my java game, it is very simply made as i am new to java. and the game works fine well as good as i can achieve. But i am stuck on how i can change the images in real time. I am trying to figure out how to make my Monsters face me "the hero frylark" when they chase me. i have made 2 simple methods in my monster class. left and right How could i apply these methods to make the image change from image = getImage("/Game/images/police-right.png"); to image = getImage("/Game/images/police-left.png");.
Oh and in my project library is golden_0_2_3.jar which contains some game engine stuff.
Please.
Many thanks from edwin.
import com.golden.gamedev.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.util.Random;
import java.awt.event.KeyEvent;
public class MyGame extends Game {
// set the values
public Random random;
private Hero frylark;
private Monster[] monsters = new Monster[3];
private Token coin;
private GameBackGround grass;
private BufferedImage image;
public void initResources() {
// set a new random number
random = new Random();
// get the background image.
image = getImage("/Game/images/background.png");
// set the name "grass" to background and given the image from the image set above.
grass = new GameBackGround("grass", image);
// get the monsters image.
image = getImage("/Game/images/police.png");
// give the monsters their names "" and set them their image from the image set above.
monsters[0] = new Monster("Monster", image);
monsters[1] = new Monster("Monster2", image);
monsters[2] = new Monster("Monster3", image);
// get the tokens image.
image = getImage("/Game/images/donut.png");
// set the name "coin" for the token, then its x and y position, and set the image from the image set above.
coin = new Token("coin", 400, 300, image);
// get the heros image.
image = getImage("/Game/images/snake.png");
// set the name "frylark" for the hero, then his score "0" and lives "5".
frylark = new Hero("Frylark", 0, 5);
//set the monsters random x and y positions.
monsters[0].setX(random.nextInt(750));
monsters[0].setY(random.nextInt(550));
monsters[1].setX(random.nextInt(750));
monsters[1].setY(random.nextInt(550));
monsters[2].setX(random.nextInt(750));
monsters[2].setY(random.nextInt(550));
}
// update method
public void update(long elapsedTime) {
// Pause the hero "frylark" on hold of the space bar.
if (!keyDown(KeyEvent.VK_SPACE)){
// if dead stop frylark moving on the 5 second game over sequence, being displays details and playing the game over sound.
if (Hero.dead(frylark)){
if(keyDown(KeyEvent.VK_LEFT))
{
// Move left
frylark.moveLeft();
}
if (keyDown(KeyEvent.VK_RIGHT))
{
// Move right
frylark.moveRight();
}
if (keyDown(KeyEvent.VK_UP))
{
// Move up on press of up key
frylark.moveUp();
}
if (keyDown(KeyEvent.VK_DOWN))
{
// Move down on press of down key
frylark.moveDown();
}
}
if (keyDown(KeyEvent.VK_ESCAPE))
{
// Exit game on press of esc key.
System.exit(0);
}
}
if (!keyDown(KeyEvent.VK_SPACE))
{
// Pause the monsters on hold of the space bar
monsters[0].chase(frylark);
monsters[1].chase(frylark);
monsters[2].chase(frylark);
}
// if monster 0 has eaten frylark move to a random position and lose a life, plus play the lose life sound.
if (monsters[0].eaten(frylark)) {
monsters[0].setX(random.nextInt(750));
monsters[0].setY(random.nextInt(550));
frylark.loseLife();
playSound("/Game/sounds/lost_a_life.wav");
}
// if monster 1 has eaten frylark move to a random position and lose a life, plus play the lose life sound.
if (monsters[1].eaten(frylark)) {
monsters[1].setX(random.nextInt(750));
monsters[1].setY(random.nextInt(550));
frylark.loseLife();
playSound("/Game/sounds/lost_a_life.wav");
}
// if monster 2 has eaten frylark move to a random position and lose a life, plus play the lose life sound.
if (monsters[2].eaten(frylark)) {
monsters[2].setX(random.nextInt(750));
monsters[2].setY(random.nextInt(550));
frylark.loseLife();
playSound("/Game/sounds/lost_a_life.wav");
}
// if coin is collected increase score and move to a random position, and play the coin collect sound.
if (coin.collected(frylark)) {
coin.setX (random.nextInt(750));
coin.setY (random.nextInt(550));
frylark.increaseScore();
playSound("/Game/sounds/coin.wav");
}
}
public void render(Graphics2D g) {
// draw all the monsters, hero, and coin and background.
g.drawImage(grass.getImage(),grass.getX(),grass.getY(),null);
g.drawImage(monsters[0].getImage(), monsters[0].GetX(), monsters[0].GetY(), null);
g.drawImage(monsters[1].getImage(), monsters[1].GetX(), monsters[1].GetY(), null);
g.drawImage(monsters[2].getImage(), monsters[2].GetX(), monsters[2].GetY(), null);
g.drawImage(image,frylark.getX(),frylark.getY(),null);
g.drawImage(coin.getImage(),coin.getX(),coin.getY(),null);
// if monster 0 overlaps another monster mover him back
if (monsters[0].overlap(monsters)){
monsters[0].x -=20;
monsters[0].y -=70;
}
// if monster 1 overlaps another monster mover him back
if (monsters[1].overlap(monsters)){
monsters[1].x -=21;
monsters[1].y -=70;
}
// if monster 2 overlaps another monster mover him back
if (monsters[2].overlap(monsters)){
monsters[2].x -=22;
monsters[2].y -=70;
}
// draw the lives bar, and set the font colour and size
g.setColor(Color.RED);
g.setFont(new Font("default", Font.BOLD, 18));
for (int i = 0; i < frylark.getLives(); i++) {
g.fillRect( (i + 1) * 15, 10, 10, 10);
}
// draw the score
g.setColor(Color.GREEN);
g.drawString("Score: " + frylark.getScore(), 10, 50);
// draw the level
g.setColor(Color.YELLOW);
g.drawString("level: " + frylark.getScoreNum(), 10, 80);
// game over sequence, changes the font to size 40 and displays game over, as well as the payers score and level reached plus the game over sound.
if (frylark.getLives() ==0){
g.setColor(Color.RED);
g.setFont(new Font("override", Font.BOLD, 40));
g.drawString("Game over !", 280, 290);
playSound("/Game/sounds/game_over.wav");
g.drawString("You reached Level " + frylark.getScoreNum() + " Your Score: " + frylark.getScore(), 60, 330);
}
}
// main method which after all classes have been read and checked, "Game development environment OK! " will be printed to the console.
// then a new game is created and given dimensions and launched.
public static void main(String args[]) {
System.out.println("Game development environment OK! ");
GameLoader gameLoader = new GameLoader();
MyGame myGame = new MyGame();
gameLoader.setup(myGame,new Dimension(800,600),false);
gameLoader.start();
}
}
and my Monster class
import java.util.Random;
import java.awt.image.BufferedImage;
public class Monster {
private String name;
int x;
int y;
private BufferedImage image;
Random rand;
public Monster (String nameIn, BufferedImage imageIn)
{
name = nameIn;
x = 0;
y = 0;
image = imageIn;
}
public void chase(Hero hero) {
if (hero.getX() < x) { // if hero is to the left
x--;
}
if (hero.getX() > x) { // if hero is to the right
x++ ;
}
if (hero.getY() < y) { // if hero is to the above
y--;
}
if (hero.getY() > y) { // if hero is to the below
y++;
}
}
public boolean overlap(Monster monsters[]){
if (monsters[0].x == monsters[1].x && monsters[0].y == monsters[1].y || monsters[0].x == monsters[2].x && monsters[0].y == monsters[2].y ||
monsters[1].x == monsters[0].x && monsters[1].y == monsters[0].y || monsters[1].x == monsters[2].x && monsters[1].y == monsters[2].y ||
monsters[2].x == monsters[0].x && monsters[2].y == monsters[0].y || monsters[2].x == monsters[1].x && monsters[2].y == monsters[1].y) {
return true;
}
else{
return false;
}
}
public boolean eaten(Hero hero) {
if (hero.getX() == x && hero.getY() == y) {
return true;
}
else {
return false;
}
}
public BufferedImage getImage() {
return image;
}
public int GetX(){
return x;
}
public int GetY(){
return y;
}
public String getName()
{
return this.name;
}
public void setX(int xIn) {
x = xIn;
}
public void setY(int yIn) {
y = yIn;
}
public boolean left(Hero hero) {
if (hero.getX() < x) {
return true;
}
else {
return false;
}
}
public boolean right(Hero hero) {
if (hero.getX() > x) {
return true;
}
else {
return false;
}
}
}

I would modify your Monster constructor to accept both images. Then modify Monster.getImage() to call left() and return the correct one based on the result. You probably don't need to call right() as well, since if the monster is not facing left then you know it needs to face right. Unless you want to get more sophisticated and also add a view facing straight forward or backward.

2D Scrolling Game: Firing Bullets. Everything runs properly theres just no image

So heres some code to begin. I first created a class called Bullet. This is where the image should be loaded.
package gameLibrary;
import java.awt.*;
import javax.swing.ImageIcon;
public class Bullet {
int x,y;
Image img;
boolean visible;
public Bullet(int startX, int startY) {
x = startX;
y = startY;
ImageIcon newBullet = new ImageIcon("/resources/bullet.png");
img = newBullet.getImage();
System.out.println("constructor Bullet is called");
visible = true;
}
public void move(){
x = x + 1;
if(x > 854){
System.out.println("Bullet is moving at X = " + x);
visible = false;
}
}
public int getX(){
return x;
}
public int getY() {
return y;
}
public boolean getVisible(){
return visible;
}
public Image getImage(){
return img;
}
}
when the space bar is pressed it calls a method called fire() where a new Bullet(X, Y); is called and then stores it in an ArrayList.
public void fire(){
if(ammo > 0) {
Bullet z = new Bullet(left + 60, y + 70);
bullets.add(z);
ammo--;
}
}
public static ArrayList getBullets(){
return bullets;
}
This code moves the bullet across the screen.
ArrayList bullets = Character.getBullets();
for(int i = 0; i < bullets.size(); i++){
Bullet m = (Bullet) bullets.get(i);
if(m.getVisible() == true){
m.move();
}if(m.getVisible() == false) {
bullets.remove(i);
}
}
And Finally code for the print method.
ArrayList bullets = Character.getBullets();
for(int i = 0; i < bullets.size(); i++){
Bullet m = (Bullet) bullets.get(0);
g2d.drawImage(m.getImage(),m.getX(),m.getY(), null);
}
I cant find where I went wrong. the functioning of the bullet is all working as far as I can tell its just the printing of the image on the screenAny suggestions is much appreciated.

Normally resources are loaded with Class.getResource
ImageIcon newBullet = new ImageIcon(Bullet.class.getResource("resources/bullet.png"));
Of course the resources folder should be in the same package (i.e. in the same folder) as your Bullet class.
That code should always work whether your game is in a jar or not.

I think your resource path is not in the good format.
ImageIcon icon = new ImageIcon("gameLibrary.resources.bullet.png");
if this doesn't work try this code to get your png path:
import java.io.File;
public class GetPath
{
public static void main(String[] args)
{
System.out.println("The user directory: " + System.getProperty("user.dir"));
File fubar = new File("Fubar.txt");
System.out.println("Where Java thinks file is located: " + fubar.getAbsolutePath());
}
}
Tell me what happens.

Debugging/fixing a BFS algorithm

I'm solving this BFS homework problem, I believe the logic I'm following is right, but I got stuck in an implementation error I can't pinpoint. I'm looking for help debugging this solution, not proposing a new one.
Problem Statement:
A kids has two robots that he controls remotely, both robots are on a NxN checkerboard and should be placed on the positions A and B in the checkerboard.
Both robots are affected by the remote controller simultaneously, the same command affects both of their states.
The remote controller can only make both robots turn clockwise or counterclockwise 90 degreees at a time or order both robots to move forward.
Example:
The leftmost image shows the initial setting. The arrow pointing right is a robot facing east and the arraw pointing up is a robot facing north. Positions A and B are the robots destinies.
Center image shows the result of moving both robots one step forward.
Right image shows the result of making the robots rotate counterclockwise.
The kid desires to calculate the minimum number of movements necessary to take the robots from their initial positions to their destinies.
If a robot is commanded to run over a wall, it will remain on the same spot.
Both robots will remain on their original spot if they're commanded to move to the same spot.
Figure 2 shows this special cases.
Both robots should at arrive at a different destiny simultaneously.
Input:
Input consists of various test cases, the first line starts with an integer with the size N of the inputMatrix (the checkerboard), with 2<= N <=25.
The following N lines describe the checkerboard and have N characters each.
A '.' indicates an empty position.
N, E, S or O (Spanish for Oeste=West) indicates the original positiona and orientation of the robot.
D indicates a destiny for the robot in the checkerboard and '*' indicates an obstacle.
Input finishes with a case where N=0.
input.txt
5
D....
N...S
.....
*...*
....D
5
.....
S..S.
.....
.....
D..D.
3
SN.
***
.DD
0
correct output for input.txt:
8
3
-1
input2.txt:
5
.....
..D.S
.D...
.....
..N..
6
......
..S...
......
.ED...
......
.D....
11
....E......
....D......
...........
..S...D....
...........
...........
...........
...........
...........
...........
...........
13
.............
.............
.............
.............
.....N.......
.............
.........D...
..D..........
.............
...E.........
.............
.............
.............
25
...*.......*.*...........
........*..D...*.**....*.
*..*.*.........*..*..*..D
...*.**.*........*...*...
......**..*..***.***...**
.............*...........
....*...***.....*.**.....
......**.......**.*.*...*
.........*..*...*.*......
....**.*.*....**.*.*.*.*.
.......*............**...
..........*.*.....*......
...........**....*.**....
.....E.*.*..........**.*.
.........*.*.*.*..*..*...
*........**...*..........
................***..*...
........*....*....*...*..
......*...*.*...*.....**.
...*..........*.**.......
.**............*.*..*.*..
........*........*...*...
*......*..........*......
*...*......N*......*..*.*
. .....*..*.*..*...*......
0
"correct" (?) output for input2.txt:
-1
-1
9
-1
46
My solution:
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;
class Position {
int i;
int j;
char orientation;
Position() {
}
void setIJ(int i, int j){
this.i=i;
this.j=j;
}
void setOrientation(char c){
orientation = c;
}
public boolean equals(Object o){
if(o instanceof Position){
Position p = (Position)o;
if((p.i==this.i)&&(p.j==this.j)&&(p.orientation==this.orientation))
{
return true;
}
else return false;
}
return false;
}
} //end class Position
class TransitionState {
Position positionA;
Position positionB;
int counter;
public boolean equals (Object o){
if (o instanceof TransitionState){
TransitionState transitionState= (TransitionState)o;
if ((this.positionA.equals(transitionState.positionA))
&&(this.positionB.equals(transitionState.positionB)))
{
return true;
}
}
return false;
}
}
public class Robots {
static Position moveForward(Position oldPosition, int matrixSize, char orientation, char [][] inputMatrix){
// add possible new Position
Position newPosition= new Position();
//first return oldPosition in border positions in which the robot shouldn't move
if ((orientation=='O')&&(oldPosition.j==0))
return oldPosition;
if ((orientation=='E')&&(oldPosition.j==(matrixSize-1)))
return oldPosition;
if ((orientation=='N')&&(oldPosition.i==0))
return oldPosition;
if ((orientation=='S')&&(oldPosition.i==(matrixSize-1)))
return oldPosition;
if ((orientation=='O'))
newPosition.setIJ(oldPosition.i, oldPosition.j-1);
if ((orientation=='E'))
newPosition.setIJ(oldPosition.i, oldPosition.j+1);
if ((orientation=='S'))
newPosition.setIJ(oldPosition.i-1, oldPosition.j);
if ((orientation=='N'))
newPosition.setIJ(oldPosition.i+1, oldPosition.j);
//return oldPosition for positions in which the robot is blocked by *
if (inputMatrix[newPosition.i][newPosition.j]=='*'){
return oldPosition;
}
return newPosition; // if it got here, all ok
}
static char turnCounter (char orientation){
if(orientation=='N')
return 'O';
if(orientation=='O')
return 'S';
if (orientation=='S')
return 'E';
else
return 'N';
}
static char turnClock(char orientation){
if(orientation=='N')
return 'E';
if(orientation=='E')
return 'S';
if (orientation=='S')
return 'O';
else
return 'N';
}
static Position[] robotInitialPositions(char [][]inputMatrix){
Position [] helperArray = new Position[2];
int aux=0;
for (int i=0; i<(inputMatrix[0].length); i++)
for (int j=0; j<(inputMatrix[0].length); j++)
{
if((inputMatrix[i][j]=='N')||(inputMatrix[i][j]=='S')||(inputMatrix[i][j]=='O')||(inputMatrix[i][j]=='E'))
{
helperArray[aux]= new Position();
helperArray[aux].setIJ(i, j);
if (inputMatrix[i][j]=='N'){helperArray[aux].orientation='N'; }
if (inputMatrix[i][j]=='S'){helperArray[aux].orientation='S'; }
if (inputMatrix[i][j]=='E'){helperArray[aux].orientation='E'; }
if (inputMatrix[i][j]=='O'){helperArray[aux].orientation='O'; }
aux= aux+1;
}
}
return helperArray;
}
static Position[] getDestinies(char [][]inputMatrix){
Position [] helperArray = new Position[2];
int aux=0;
for (int i=0; i<(inputMatrix[0].length); i++)
for (int j=0; j<(inputMatrix[0].length); j++)
{
if((inputMatrix[i][j]=='D'))
{
helperArray[aux]= new Position();
helperArray[aux].i=i; helperArray[aux].j=j;
helperArray[aux].orientation='D';
aux=aux+1;
}
}
return helperArray;
}
static boolean [][]getUnvisitedMatrix(int matrixLength){
boolean[][] unvisitedMatrix = new boolean [matrixLength][matrixLength];
for (int i=0; i<matrixLength;i++)
for (int j=0; j<matrixLength; j++)
unvisitedMatrix[i][j]=false;
return unvisitedMatrix;
}
static Position[]getNewRobotPositions (Position oldR1Pos,Position oldR2Pos, String movement, char [][]inputMatrix){
Position[]newPositions = new Position[2];
Position newR1Pos = new Position();
Position newR2Pos = new Position();
if(movement.equals("counter")){
if (oldR1Pos.orientation=='N'){
newR1Pos.orientation='O';
}
if (oldR1Pos.orientation=='S'){
newR1Pos.orientation='E';
}
if (oldR1Pos.orientation=='E'){
newR1Pos.orientation='N';
}
if (oldR1Pos.orientation=='O'){
newR1Pos.orientation='S';
}
if (oldR2Pos.orientation=='N'){
newR2Pos.orientation='O';
}
if (oldR2Pos.orientation=='S'){
newR2Pos.orientation='E';
}
if (oldR2Pos.orientation=='E'){
newR2Pos.orientation='N';
}
if (oldR2Pos.orientation=='O'){
newR2Pos.orientation='S';
}
newR1Pos.i=oldR1Pos.i;
newR1Pos.j=oldR1Pos.j;
newR2Pos.i=oldR2Pos.i;
newR2Pos.j=oldR2Pos.j;
newPositions[0]=newR1Pos;
newPositions[1]=newR2Pos;
// System.out.println("MOVED COUNTERCLOCKWISE");
// System.out.println("previous Robot 1 position was "+oldR1Pos.i + ","+oldR1Pos.j + " orientation was " + oldR1Pos.orientation +
// " new Robot 1 position is " + newR1Pos.i + "," + newR1Pos.j+ " orientation is "+newR1Pos.orientation);
//
// System.out.println("previous Robot 2 position was "+oldR2Pos.i + ","+oldR2Pos.j + " orientation was " + oldR2Pos.orientation +
// " new Robot 2 position is " + newR2Pos.i + "," + newR2Pos.j+ " orientation is "+newR2Pos.orientation);
return newPositions;
}
if(movement.equals("clock")){
newR1Pos.i = oldR1Pos.i;
newR1Pos.j = oldR1Pos.j;
newR2Pos.i = oldR2Pos.i;
newR2Pos.j = oldR2Pos.j;
if (oldR1Pos.orientation=='N'){
newR1Pos.orientation= 'E';
}
if (oldR1Pos.orientation=='S'){
newR1Pos.orientation= 'O';
}
if (oldR1Pos.orientation=='E'){
newR1Pos.orientation= 'S';
}
if (oldR1Pos.orientation=='O'){
newR1Pos.orientation= 'N';
}
if (oldR2Pos.orientation=='N'){
newR2Pos.orientation= 'E';
}
if (oldR2Pos.orientation=='S'){
newR2Pos.orientation= 'O';
}
if (oldR2Pos.orientation=='E'){
newR2Pos.orientation= 'O';
}
if (oldR2Pos.orientation=='O'){
newR2Pos.orientation= 'N';
}
// System.out.println("MOVED CLOCKWISE");
// System.out.println("previous Robot 1 position was "+oldR1Pos.i + ","+oldR1Pos.j + " orientation was " + oldR1Pos.orientation +
// " new Robot 1 position is " + newR1Pos.i + "," + newR1Pos.j+ " orientation is "+newR1Pos.orientation);
/ /
// System.out.println("previous Robot 2 position was "+oldR2Pos.i + ","+oldR2Pos.j + " orientation was " + oldR2Pos.orientation +
// " new Robot 2 position is " + newR2Pos.i + "," + newR2Pos.j+ " orientation is "+newR2Pos.orientation);
newPositions[0]=newR1Pos;
newPositions[1]=newR2Pos;
return newPositions;
}
if(movement.equals("forward")){
//default case, if conditions not satisfied
newR1Pos.i=oldR1Pos.i;
newR1Pos.j=oldR1Pos.j;
newR1Pos.orientation = oldR1Pos.orientation;
newR2Pos.i=oldR2Pos.i;
newR2Pos.j=oldR2Pos.j;
newR2Pos.orientation = oldR2Pos.orientation;
if(oldR1Pos.orientation=='N'){
if(oldR1Pos.i-1>=0){ //doesn't exceed the upper border
//doesn't collide with '*'
if (inputMatrix[oldR1Pos.i-1][oldR1Pos.j]!='*'){
newR1Pos.i=oldR1Pos.i-1;
newR1Pos.j=oldR1Pos.j;
newR1Pos.orientation = oldR1Pos.orientation;
}
}
}
if(oldR1Pos.orientation=='S'){
if(oldR1Pos.i+1<inputMatrix.length){ //doesn't exceed the lower border
//doesn't collide with '*'
if (inputMatrix[oldR1Pos.i+1][oldR1Pos.j]!='*'){
newR1Pos.i=oldR1Pos.i+1;
newR1Pos.j=oldR1Pos.j;
newR1Pos.orientation = oldR1Pos.orientation;
}
}
}
if(oldR1Pos.orientation=='E'){
if(oldR1Pos.j+1<inputMatrix.length){ //doesn't exceed the right border
//doesn't collide with '*'
if (inputMatrix[oldR1Pos.i][oldR1Pos.j+1]!='*'){
newR1Pos.i=oldR1Pos.i;
newR1Pos.j=oldR1Pos.j+1;
newR1Pos.orientation = oldR1Pos.orientation;
}
}
}
if(oldR1Pos.orientation=='O'){
if(oldR1Pos.j-1>=0){ //doesn't exceed the left border
//doesn't collide with '*'
if (inputMatrix[oldR1Pos.i][oldR1Pos.j-1]!='*'){
newR1Pos.i=oldR1Pos.i;
newR1Pos.j=oldR1Pos.j-1;
newR1Pos.orientation = oldR1Pos.orientation;
}
}
}
//same for robot 2
if(oldR2Pos.orientation=='N'){
if(oldR2Pos.i-1>=0){ //doesn't exceed the upper border
//doesn't collide with '*'
if (inputMatrix[oldR2Pos.i-1][oldR2Pos.j]!='*'){
newR2Pos.i=oldR2Pos.i-1;
newR2Pos.j=oldR2Pos.j;
newR2Pos.orientation=oldR2Pos.orientation;
}
}
}
if(oldR2Pos.orientation=='S'){
if(oldR2Pos.i+1<inputMatrix.length){ //doesn't exceed the lower border
//doesn't collide with '*'
if (inputMatrix[oldR2Pos.i+1][oldR2Pos.j]!='*'){
newR2Pos.i=oldR2Pos.i+1;
newR2Pos.j=oldR2Pos.j;
newR2Pos.orientation=oldR2Pos.orientation;
}
}
}
if(oldR2Pos.orientation=='E'){
if(oldR2Pos.j+1<inputMatrix.length){ //doesn't exceed the right border
//doesn't collide with '*'
if (inputMatrix[oldR2Pos.i][oldR2Pos.j+1]!='*'){
newR2Pos.i=oldR2Pos.i;
newR2Pos.j=oldR2Pos.j+1;
newR2Pos.orientation=oldR2Pos.orientation;
}
}
}
if(oldR2Pos.orientation=='O'){
if(oldR2Pos.j-1>=0){ //doesn't exceed the left border
//doesn't collide with '*'
if (inputMatrix[oldR2Pos.i][oldR2Pos.j-1]!='*'){
newR2Pos.i=oldR2Pos.i;
newR2Pos.j=oldR2Pos.j-1;
newR2Pos.orientation=oldR2Pos.orientation;
}
}
}
//if robots collide in new positions, revert to their original positions
if ((newR1Pos.i==newR2Pos.i) && (newR1Pos.j==newR2Pos.j)){
//revert robot 1 position
newR1Pos.i=oldR1Pos.i;
newR1Pos.j=oldR1Pos.j;
newR1Pos.orientation = oldR1Pos.orientation;
//revert robot 2 position
newR2Pos.i=oldR2Pos.i;
newR2Pos.j=oldR2Pos.j;
newR2Pos.orientation = oldR2Pos.orientation;
}
newPositions[0] = newR1Pos;
newPositions[1] = newR2Pos;
// System.out.println("MOVED FORWARD");
// System.out.println("previous Robot 1 position was "+oldR1Pos.i + ","+oldR1Pos.j + " orientation was " + oldR1Pos.orientation +
// " new Robot 1 position is " + newR1Pos.i + "," + newR1Pos.j+ " orientation is "+newR1Pos.orientation);
//
// System.out.println("previous Robot 2 position was "+oldR2Pos.i + ","+oldR2Pos.j + " orientation was " + oldR2Pos.orientation +
// " new Robot 2 position is " + newR2Pos.i + "," + newR2Pos.j+ " orientation is "+newR2Pos.orientation);
} //end movement.equals("forward")
return newPositions;
}
//1 procedure BFS(Graph,source):
//2 create a queue Q
//3 enqueue source onto Q
//4 mark source
//5 while Q is not empty:
//6 dequeue an item from Q into v
//7 for each edge e incident on v in Graph:
//8 let w be the other end of e
//9 if w is not marked:
//10 mark w
//11 enqueue w onto Q
static void BFS (char [][] inputMatrix){
ArrayList<TransitionState> transitionStatesArray = new ArrayList<TransitionState>();
int moveCounter=0; //turns and forward movements add here
int tempMoveCounterRobot1=0; int tempMoveCounterRobot2=0;
int maxMoveCounter=0;
PositionsAndCounter positionsAndCounter= new PositionsAndCounter();
Queue <PositionsAndCounter>queue = new LinkedList<PositionsAndCounter>();
Position robotInitial[] = robotInitialPositions(inputMatrix); //get source
positionsAndCounter.positionPair=robotInitial; //used to encapsulate the positions with a counter to output
positionsAndCounter.counter=0;//first initialize to 0
Position destinies[] = getDestinies(inputMatrix); //get destinies
TransitionState firstTransitionState = new TransitionState();
firstTransitionState.positionA=robotInitial[0];
firstTransitionState.positionB=robotInitial[1];
transitionStatesArray.add(firstTransitionState);
//mark transition used , if the transition is new, it should be queued
queue.add(positionsAndCounter);
String [] movement = {"forward", "counter", "clock"};
//possible movements inside inputMatrix
outer: while (!queue.isEmpty()){ //while queue is not empty
PositionsAndCounter v= queue.poll(); //dequeue an item from Q into V
for(int k = 0; k<3; k++){ //for each edge e incident on v in Graph:
Position[] newRobotPositions = getNewRobotPositions(v.positionPair[0], v.positionPair[1], movement[k], inputMatrix);
TransitionState newTransitionState = new TransitionState();
newTransitionState.positionA=newRobotPositions[0];
newTransitionState.positionB=newRobotPositions[1];
if(!transitionStatesArray.contains(newTransitionState)){ //if the transition state is new add and enqueue new robot positions
transitionStatesArray.add(newTransitionState);
//if transition is new then queue
PositionsAndCounter newPositionsAndCounter = new PositionsAndCounter();
newPositionsAndCounter.positionPair=newRobotPositions;
newPositionsAndCounter.counter = v.counter +1;
queue.add(newPositionsAndCounter);
}
inputMatrix[v.positionPair[0].i][v.positionPair[1].j]='.';
inputMatrix[v.positionPair[1].i][v.positionPair[1].j]='.';
//inputMatrix[v[0].i][v[0].j]='.'; // mark old position of robot 1 with .
//inputMatrix[v[1].i][v[1].j]='.'; // mark old position of robot 2 with .
//update new robot positions
inputMatrix[newRobotPositions[0].i][newRobotPositions[0].j]= newRobotPositions[0].orientation;
inputMatrix[newRobotPositions[1].i][newRobotPositions[1].j]= newRobotPositions[1].orientation;
//check if solution has been found
if
(
((destinies[0].i==newRobotPositions[0].i)&&(destinies[0].j==newRobotPositions[0].j) //robot in 0 arrived to destiny
|| (destinies[1].i==newRobotPositions[0].i)&&(destinies[1].j==newRobotPositions[0].j))// in 0 or 1
&& //and
((destinies[0].i==newRobotPositions[1].i)&&(destinies[0].j==newRobotPositions[1].j) //robot in 1 arrived to destiny
|| (destinies[1].i==newRobotPositions[0].i)&&(destinies[1].j==newRobotPositions[0].j))//in 0 or 1
) //end if
{
System.out.println("robots arrived at destinies");
System.out.println("robot 1, starting at " + robotInitial[0].i + "," + robotInitial[0].j
+ " is in " + newRobotPositions[0].i + ","+ newRobotPositions[0].j);
System.out.println("robot 2, starting at " + robotInitial[1].i + "," + robotInitial[1].j
+ " is in " + newRobotPositions[1].i + ","+ newRobotPositions[1].j);
System.out.println("movements: " + (v.counter));
return;
//break outer;
}
}
}
System.out.println("robots can never arrive at their destinies");
System.out.println(-1);
}
static void printInputMatrix(char [][] inputMatrix){
for (int i=0; i<inputMatrix[0].length;i++)
for(int j=0; j<inputMatrix[0].length;j++)
{
System.out.print(" "+inputMatrix[i][j]+" ");
if(j==inputMatrix[0].length-1){System.out.println("");}
}
}
public static void main(String[] args) throws IOException {
// System.out.println("Test transition checker");
// Position p1 = new Position();
// p1.i=1;
// p1.j=1;
// p1.orientation='N';
// Position p2 = new Position();
// p2.i=1;
// p2.j=2;
// p2.orientation='N';
// Position p3 = new Position();
// p3.i=1;
// p3.j=1;
// p3.orientation='N';
// Position p4 = new Position();
// p4.i=1;
// p4.j=1;
// p4.orientation='N';
//
// TransitionState transitionChecker1 = new TransitionState();
// transitionChecker1.positionA=p1;
// transitionChecker1.positionB=p2;
//
// TransitionState transitionChecker2 = new TransitionState();
// transitionChecker2.positionA=p1;
// transitionChecker2.positionB=p2;
//
//
// ArrayList<TransitionState> arrayTransitions = new ArrayList<TransitionState>();
// arrayTransitions.add(transitionChecker1);
// System.out.println("Test contains? " + arrayTransitions.contains(transitionChecker2));
BufferedReader br = new BufferedReader(new FileReader(new File("input.txt")));
char [][] inputMatrix;
String line;
char [] lineAsCharArray;
int matrixSize;
while(true){
line = br.readLine();
matrixSize=Integer.parseInt(line);
inputMatrix = new char [matrixSize][matrixSize];
if (matrixSize==0){ // end outer looping
break;
}
else { //begin inner looping
for (int i=0; i<matrixSize; i++){
line = br.readLine();
inputMatrix[i] =line.toCharArray();
}
//matrix loaded
BFS(inputMatrix);
}
}
}
}
class PositionsAndCounter {
Position[] positionPair;
int counter;
PositionsAndCounter() {
positionPair = new Position[2];
counter=0;
}
}
Problems:
1) On the first input.txt file, it finds 9 movements to find the solution of the first course (when they should be 8) and 6 to find the solution of the second course (when it should be 3) though it correctly prints out -1 for the last (impossible) course configuration.
2) On the second input.txt file, professor says it should print -1 and -1 for the to first courses, though my program finds a plaussible solution for the second case and a bizarre one for the first (this is where I think a more experienced debugger could help, I'm at a loss tracking the reason for the displaced destiny output on the first case). Are the outputs proposed by my professor right? My algorithm is also getting stuck on that case where 46 should be printed.

The are 2 careless copy and paste problems causes the code not working,
1, in the clockwise turning part:
if (oldR2Pos.orientation == 'E') {
newR2Pos.orientation = 'O';
}
This is wrong... it should be a direct copy and paste from the above block
if (oldR2Pos.orientation == 'E') {
newR2Pos.orientation = 'S';
}
Yet you missed it.
Another problem is actually in the end condition testing block
//check if solution has been found
if
(
((destinies[0].i==newRobotPositions[0].i)&&(destinies[0].j==newRobotPositions[0].j) //robot in 0 arrived to destiny
|| (destinies[1].i==newRobotPositions[0].i)&&(destinies[1].j==newRobotPositions[0].j))// in 0 or 1
&& //and
((destinies[0].i==newRobotPositions[1].i)&&(destinies[0].j==newRobotPositions[1].j) //robot in 1 arrived to destiny
|| **(destinies[1].i==newRobotPositions[0].i)&&(destinies[1].j==newRobotPositions[0].j)**)//in 0 or 1
) //end if
The last part (code highlighted) should be
(destinies[1].i==newRobotPositions[1].i)&&(destinies[1].j==newRobotPositions[1].j)
It is obviously an copy and paste but forget to change error. The logic is a little bit hard to understand, but works,
(A in X or B in Y) and (A in Y or B in X)
Although it is the same (logically not exactly the same but it some how works for your case as A and B cannot occupy the same location), it is much clearer if you use
(A in X and B in Y) or (A in Y and B in X)
Apart from the fatal errors stated above, your program has a few other issues need to addressed.It looks like you are a university student taking Computer science, please, read the given source code before coding: TransistionState class is not used at all but you created your own PositionsAndCounter, turning logic is implemented twice, if you didn't rewrite the turning code, and use the one given, you won't commit problem 1.... If I were your professor, i may fail you on that. Plan your solution well before hitting the keyboard, and make sure your code is clear and readable as plan english, if you stare at your source code for 5 min and cannot figure out what the block of code is for, may be you didn't structure it correctly.
The listing below is an example solution for your question:
import java.awt.Point;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
public class DualRobot {
public enum Orientation{
E(1, 0), S(0, 1), O(-1, 0), N(0, -1);
public final int dx, dy;
private Orientation(int dx, int dy){
this.dx = dx;
this.dy = dy;
}
public Orientation left(){
return Orientation.values()[(this.ordinal() + 3) % 4];
}
public Orientation right(){
return Orientation.values()[(this.ordinal() + 1) % 4];
}
public static Orientation valueOf(char c){
for(Orientation o : Orientation.values()){
if(o.toString().equalsIgnoreCase("" + c)) return o;
}
return null;
}
}
public enum Action {FORWARD, COUNTER_CLOCKWISE, CLOCKWISE}; // F: forward, L: Counter clockwise, R: clockwise
private static class Robot{
Point position;
Orientation orientation;
public Robot(Robot r){
this.position = new Point(r.position);
this.orientation = r.orientation;
}
public Robot(int x, int y, Orientation orientation){
this.position = new Point(x, y);
this.orientation = orientation;
}
public void move(Action action, char[][] map){
switch (action) {
case FORWARD:
Point nextPosition = new Point(position);
nextPosition.translate(orientation.dx, orientation.dy);
if(isValidPosition(nextPosition, map)) position = nextPosition;
break;
case COUNTER_CLOCKWISE:
this.orientation = this.orientation.left();
break;
case CLOCKWISE:
this.orientation = this.orientation.right();
break;
}
}
#Override
public boolean equals(Object obj) {
if (obj instanceof Robot) {
Robot r = (Robot) obj;
return r.position.equals(this.position) && r.orientation == this.orientation;
}
return super.equals(obj);
}
#Override
public int hashCode() {
return orientation.ordinal() + position.x * 10 + position.y * 1000;
}
private boolean isValidPosition(Point p, char[][] map){
return p.x >= 0 && p.x < map[0].length
&& p.y >= 0 && p.y < map.length
&& map[p.y][p.x] != '*';
}
}
private static class State{
private Robot a, b;
private int counter;
public State(Robot a, Robot b, int counter) {
this.a = new Robot(a);
this.b = new Robot(b);
this.counter = counter;
}
public List<State> nextStates(char[][] map){
List<State> states = new ArrayList<State>();
for(Action action : Action.values()){
State s = new State(this.a, this.b, this.counter + 1);
s.a.move(action, map);
s.b.move(action, map);
if(!s.a.position.equals(s.b.position)){ // Test for collision
states.add(s);
}
}
return states;
}
#Override
public boolean equals(Object obj) {
if (obj instanceof State) {
State state = (State) obj; // Consider the state to be the same if the 2 robots are at identical location and orientation
return (this.a.equals(state.a) && this.b.equals(state.b))
|| (this.a.equals(state.b) && this.b.equals(state.a));
}
return super.equals(obj);
}
#Override
public int hashCode() {
// The quality of this hashCode can affect the program's speed
// Multiply is transitive, so if you swap a and b, the hashcode is the same
return a.hashCode() * b.hashCode();
}
}
public static void main(String[] args) throws IOException {
BufferedReader input = new BufferedReader(new FileReader("input.txt"));
int size;
while((size = Integer.parseInt(input.readLine())) > 0){
// Load the data;
char[][] map = new char[size][size];
for (int i = 0; i < size; i++) {
map[i] = input.readLine().toCharArray();
}
// Construct initial state
List<Robot> robots = new ArrayList<Robot>();
List<Point> destinations = new ArrayList<Point>();
for(int i = 0; i < size; i ++){
for(int j = 0; j < size; j ++){
Orientation orientation = Orientation.valueOf(map[i][j]);
if(orientation != null){
robots.add(new Robot(j, i, orientation));
}else if(map[i][j] == 'D'){
destinations.add(new Point(j, i));
}
}
}
System.out.println(BFSSearch(map, new State(robots.get(0), robots.get(1), 0), destinations));
}
}
private static int BFSSearch(char[][] map, State initialState, List<Point> destinations) throws IOException{
List<State> queue = new LinkedList<State>(); // Array list is slightly more efficient
queue.add(initialState); // Initial state
Map<State, Boolean> testedStates = new HashMap<State, Boolean>();
while(queue.size() > 0){
State currentState = queue.remove(0);
if(testedStates.containsKey(currentState)) continue;
// Testing for end condition
if((currentState.a.position.equals(destinations.get(0)) && currentState.b.position.equals(destinations.get(1)))
|| (currentState.a.position.equals(destinations.get(1)) && currentState.b.position.equals(destinations.get(0)))){
return currentState.counter;
}
testedStates.put(currentState, true);
queue.addAll(currentState.nextStates(map));
}
return -1;
}
}
This program spit out the final answer in around 10 seconds.
The main difference is I used an hash table to store the tested states to improve the speed, thus the quality of the hash function would have an effect on the speed.
Recommended reading: hash table, DRY principle.