Develop Reference

Printing randomly fed values from an ArrayList in Java

I am processing elements of an ArrayList in random order, generally by printing them out. I would like to detect when the randomly selected index is 0 or 1 so as to perform special handling for those cases, where the handling for index 0 is partially dependent on whether index 1 has previously been processed. Specifically, nothing is immediately printed when index 1 is processed, but if it is processed then when index 0 is subsequently processed, both the index 1 and the index 0 values are printed. In any event, the loop is exited after ten iterations or after processing index 0, whichever comes first.
I tried to implement this using if statements, but there where obvious flaws with that one. I have searched everywhere for any examples but found none. I have begun to consider using sorting algorithms or threads to hold the first value found then continue looping until it sees the second the print it out. I would appreciate any help possible.
Here is my code:
public static void random_sortType(){
types = new ArrayList<String>();
types.add("Start");
types.add("Starting");
types.add("Load");
types.add("Loading");
types.add("End");
ran = new Random();
int listSize = types.size();
String tempEventType;//the temp variable intended to hold temporary values
for(int i = 0; i < 10; i++){ //the loop goes round the ArrayList 10 times
int index = ran.nextInt(listSize);//this produces the random selection of the elements within the list
if(index == 0){
out.println(types.get(index));
out.println();
break;
}
if(index == 1){
tempEventType = types.get(index);
if(index == 0){
tempEventType = types.get(0) + " " + types.get(1);
out.println(tempEventType);
break;
}
}/*if(index == 0){
tempEventType = types.get(0) + " " + types.get(1);
out.println(tempEventType);
break;
}*/
//out.print("Index is " + index + ": ");
//out.println(types.get(index));
}
}

You need to store the random generated index into a global variable and update it everytime a random number is generated. It should be something like this.
public static void random_sortType(){
types = new ArrayList<String>();
types.add("Start");
types.add("Starting");
types.add("Load");
types.add("Loading");
types.add("End");
` int previousIndex;
ran = new Random();
int listSize = types.size();
String tempEventType;//the temp variable intended to hold temporary values
for(int i = 0; i < 10; i++){ //the loop goes round the ArrayList 10 times
int index = ran.nextInt(listSize);//this produces the random selection of the elements within the list
previous_index =index;
if(index == 0){
out.println(types.get(index));
out.println();
break;
}
if(index == 1){
tempEventType = types.get(index);
if(previousIndex == 0){
temp EventType = types.get(0) + " " + types.get(1);
out.println(tempEventType);
break;
}

According to your description, these are the basic requirements for your application:
Process ArrayList in random order
Processing = printing value at randomly selected index
Make 10 attempts to process items in the list.
Detect when random index is 1 or 0.
if 1
don't process, but flag it was selected.
if 0 && 1 is flagged
process 0 and 1
exit
If these requirements are correct, here is the implementation I came up with:
import java.util.ArrayList;
import java.util.Random;
import static java.lang.System.*;
public class RandomSort {
private static final int MAX_ATTEMPTS = 10;
private static boolean wasOneSelected = false;
public static void main(String[] args) {
ArrayList<String> types = new ArrayList<>(5);
types.add("Start");
types.add("Starting");
types.add("Load");
types.add("Loading");
types.add("End");
random_sortType(types);
}
public static void random_sortType(ArrayList<String> types) {
Random ran = new Random();
int lastIndex = types.size() - 1; // index range is from 0 to 4
for (int i = 0; i < MAX_ATTEMPTS; i++) {
int index = ran.nextInt(lastIndex);
if ( (index == 0) && wasOneSelected) {
process(types.get(index) + " " + types.get(index + 1));
break;
} else if (index == 1) {
wasOneSelected = true;
} else {
process(types.get(index));
}
}
}
public static void process(String str) {
out.println("Processing: " + str);
}
}
The key here is the inclusion of the boolean wasOneSelected initialized to false. Once it is set to true, it will never be false again for the duration of the application. The if-else block handles all branching within the loop, and I favored wrapping the println call into a method called "process" for readability purposes to align it more closely with your description.
Feedback appreciated :)

Weird behavior in Java While Loop [duplicate]

This question already has an answer here:
Loop doesn't see value changed by other thread without a print statement
(1 answer)
Closed 7 years ago.
I am writing a basic Tic-Tac-Toe Single player game using basic swing graphics. I completed the game, but there is a weird problem I am facing. At one place, I used a while loop with a SOP statement. If I omit this statement, program works differently and nothing happens (like some kind of infinite loop), and if I keep it, it works just fine. I don't know what's happening in the code. Please help.
Below is the source code which causing problem. Sorry for my amateur coding style.
import java.util.Random;
public class SinglePlayer implements Runnable{
public final int MINIMUM = -1000000;
private GameBoard game;
public SinglePlayer(){
game = new GameBoard("Single Player");
}
public static void main(String[] args){
SinglePlayer gameSingle = new SinglePlayer();
gameSingle.run();
}
public void run(){
boolean machinePlayed = true, userPlayed = false;
// Outer loop is to maintain re-match option of program
while(this.game.quitTwoPlayer == false){
// Inner loop is a single game b/w user and machine
while(this.game.GameQuitStatus() == false){
/* I kept two conditions to switch b/w machine and user mode
* of game and they just keep changing to simulate the game
* b/w machine and user.
*/
if(machinePlayed == false && userPlayed){
try {
MachineMove("O");
} catch (CloneNotSupportedException e) {
e.printStackTrace();
break;
}
this.game.ChangePlayerLabels();
machinePlayed = true;
userPlayed = false;
}
else if(machinePlayed && userPlayed == false){
int earlierCount = this.game.CountSteps();
/* THIS IS THE WHILE LOOP I AM TALKING ABOUT.
* If I omit the print statement inside the body of loop,
* program behaves differently, but when I keep it,
* it working just fine.
* */
while(earlierCount == this.game.CountSteps()){
System.out.println("Player User thinking");
}
this.game.ChangePlayerLabels();
machinePlayed = false;
userPlayed = true;
}
this.game.DeclareResult();
}
this.game.dispose();
}
}
public void MachineMove(String player) throws CloneNotSupportedException{
/* If board is empty, play at center of the board */
if(this.game.CountSteps() == 0){
this.game.MakeMove(1, 1);
}
/* If center is blank, play it there. Otherwise, pick a corner randomly */
else if(this.game.CountSteps() == 1){
if(this.game.IsEmpty(1, 1))
this.game.MakeMove(1, 1);
else{
Random randomNum = new Random();
int num = randomNum.nextInt(4);
if(num == 0)
this.game.MakeMove(0, 0);
else if(num == 1)
this.game.MakeMove(2, 0);
else if(num == 2)
this.game.MakeMove(0, 2);
else if(num == 3)
this.game.MakeMove(2, 2);
}
}
else{
/* If the next move is such that it should be taken, otherwise opponent will win */
String opponent = "";
if(this.game.GetCurrentPlayer().equals("O"))
opponent = "X";
else
opponent = "O";
for(int i = 0; i<3; i++){
for(int j = 0; j<3; j++){
if(this.game.IsEmpty(i,j)){
GameBoard tempGame = new GameBoard(this.game, "Single Player");
tempGame.MakePossibleMove(i, j, opponent);
if(tempGame.GameWinner().equals(opponent + " wins")){
this.game.MakeMove(i,j);
return;
}
}
}
}
/* If the next move is not such that if missed, game is lost, then play most optimal move towards winning */
Move tempMove = new Move(MINIMUM, 0, 0);
Move bestMove = new Move(MINIMUM, 0, 0);
for(int i = 0; i<3; i++){
for(int j = 0; j<3; j++){
if(this.game.IsEmpty(i,j)){
GameBoard tempGame = new GameBoard(this.game, "Single Player");
tempMove = MakeMoves(tempGame, i, j);
if(tempMove.score > bestMove.score){
bestMove.row = tempMove.row;
bestMove.col = tempMove.col;
bestMove.score = tempMove.score;
}
}
}
}
this.game.MakeMove(bestMove.row, bestMove.col);
}
}
public Move MakeMoves(GameBoard tempGame, int row, int col){
String player = tempGame.GetCurrentPlayer();
tempGame.MakeMove(row, col);
if(tempGame.GameWinner().equals("Match Draw")){
return new Move(0, row, col);
}
else if(tempGame.GameWinner().equals("X wins")){
if(player.equals("X")){
return new Move(1, row, col);
}
else{
return new Move(-1, row, col);
}
}
else if(tempGame.GameWinner().equals("O wins")){
if(player.equals("O")){
return new Move(1, row, col);
}
else{
return new Move(-1, row, col);
}
}
else{
Move bestMove = new Move(MINIMUM, 0, 0);
Move tempBestMove = new Move(0, 0, 0);
for(int i = 0; i<3; i++){
for(int j = 0; j<3; j++){
if(tempGame.IsEmpty(i,j)){
GameBoard newGame = new GameBoard(tempGame, "Single Player");
tempBestMove = MakeMoves(newGame, i, j);
if(tempBestMove.score > bestMove.score)
bestMove = tempBestMove;
}
}
}
return bestMove;
}
}
}
class Move{
public int score;
public int row;
public int col;
public Move(int score, int row, int col){
this.score = score;
this.row = row;
this.col = col;
}
}

Your loop is likely typing up your processor, and the SOP slows the loop enough to allow other processes to occur. But regardless and most importantly, you don't want to have this loop present in the first place. You state that you have a,
Tic-Tac-Toe Single player game using basic swing graphics
Remember that Swing is an event driven GUI library, so rather than loop as you would in a linear console program, let events occur, but respond to them based on the state of the program.
In other words, give your class several fields including a boolean variable that tells whose turn it is, such as boolean playersTurn, a boolean variable gameOver, ..., and change the state of these variables as the game is played, and base the games behavior depending on these states. For instance the game would ignore the player's input if it was not his turn.

Some issue with an enhanced for loop-SimpleDotCom

This is a modified example from the book, Head First Java. It's a kind of Battleship game where a 3 element array is being used as the battleship. The user has to guess these 3 locations. Currently, I've hard-coded the values of the ship location to 2,3,4. When the user guesses the correct location "Hit" is printed. If not then "Miss" is printed. If a user guesses all 3 locations then "Kill" is printed. But I have a problem. Currently if the user enters the same location multiple times, it still gives a hit. I tried to fix this by changing the value of a variable that has already been hit (int cell) to "-1". But for some reason this didn't fix it too. Please tell me what I am doing wrong.
public class Game {
public static void main(String[] args) {
// TODO Auto-generated method stub
int [] location = {2,3,4};
SimpleDotCom firstGame = new SimpleDotCom();
firstGame.setLocation(location);
firstGame.checkYourself("2");
firstGame.checkYourself("2");
//firstGame.checkYourself("2");
}
}
public class SimpleDotCom {
int [] loc = null;
int numOfHits = 0;
void setLocation (int [] cellLocation){
loc = cellLocation;
}
void checkYourself(String userGuess){
int guess = Integer.parseInt(userGuess);
String result = "Miss";
for(int cell:loc){
if (guess == cell){
result = "Hit";
numOfHits++;
cell = -1;
break;
}
if (numOfHits==loc.length){
result = "Kill";
}
}
System.out.print("Result: " + result);
System.out.println(" ** Num of Hits: " + numOfHits);
}
}

When you loop over loc, you get an int cell for each location. The problem is that that variable doesn't have any connection to the array, it's only a copy. If you change it, nothing's going to happen to the original array. I suggest looping over loc with a traditional for(;;) and using the current array index within the loop's logic to set the right "cells" to -1.

because you are assigning -1 to local variable. not updating in array actually
for(int cell:loc){ // cell is local copy of element in array is you have array of primitive int
if (guess == cell){
result = "Hit";
numOfHits++;
cell = -1;
break;
}
if (numOfHits==loc.length){
result = "Kill";
}
}
You can use traditional for loop for this or use List which has methods for adding removing elements.

You need to update the array at the correct index, not simply change the value of the cell variable, which only references the array element at the current iteration state.
You should probably use a traditionnal for loop for that, since you cannot get the index for free from an enhanced for loop.
for (int i = 0; i < loc.length; i++) {
//code...
loc[i] = -1; //instead of cell = -1;
}

How do I pass an array to a method in java?

Here is the program that I am trying to run:
/**
* Write a description of class mainGame here.
*
* #author Anthony Parsch
* #version 0.1.1
*/
//Import what I need to.
import java.io.*;
public class mainGame
{
/**
* Constructor for objects of class mainGame
*/
public static void main(String[] args)
{
// initialise instance variables
int xCoord = 10; //The map's max x coordinate +1
int yCoord = 10; //The map's max y coordinate +1
int playerX = 0; //The player's current x coordinate
int playerY = 0; //The player's current y coordinate
//Declare the arrays
String[][] map; //[x][y]The map
String[][] direc; //[x][y]Which directions that you can go
String[][] items; //[x][y]Where items are at
String[] inv; // Holds your inventory.
int[][] helpInt; //[x][y] All the other stuff in the
//Initalize the arrays
//---The player arrays
inv = new String[10]; //The player's inventory
inv[0] = "0";
inv = addItem(inv, "Blarg");//GET RID OF THIS LATER
//---The map arrays
map = new String[xCoord][yCoord]; //Descriptions
direc = new String[xCoord][yCoord]; //north y++,west x--,south y--,east x++
items = new String[xCoord][yCoord]; //The items within the world
//Declare the values of map
map[0][0] = "You wake up with the feel of cold metal on your back. The only other thing in this room is the door.";
map[0][1] = "You are now in a hallway with a door behind you and one either side. Forward is a continuation of the hallway.com";
//Declare the values of direc
direc[0][0] = "north";
direc[0][1] = "north, south, east, west";
print(inv[0]); //Check that the functions work
print(findDirec(direc, 0, 0));
}
/**
* Finds and displays the avaliable exits for a coordinate.
*
* #param map[][] The map array from which this method pulls the directions from.
* #param x The x value of the map
* #param y The y value of the map
* #return The string value of which way you can go
*/
static String findDirec(String[][] map, int x, int y){
//Pulls the directions
String match = map[x][y];
//Checks Directions
boolean nor = match.matches("(.*)north(.*)");
boolean sou = match.matches("(.*)south(.*)");
boolean wes = match.matches("(.*)west(.*)");
boolean eas = match.matches("(.*)east(.*)");
//Displays directions
String placeHolder = "You can go ";
if (nor == true){
placeHolder = placeHolder + "north, ";
} else if(sou == true) {
placeHolder = placeHolder + "south, ";
} else if(wes == true) {
placeHolder = placeHolder + "west, ";
} else if(eas == true) {
placeHolder = placeHolder + "east";
}
//---Checks if east is in the string, if not it removes the space and comma
if (eas == false){
StringBuffer soo = new StringBuffer(placeHolder);
soo.delete((placeHolder.length()-3), (placeHolder.length()-1));
placeHolder = soo.toString();
}
//Adds the ending period
placeHolder = placeHolder + ".";
//Returns the string
return placeHolder;
}
//Adds an item to an inventory
static String[] addItem(String inv[], String item){
int i; //Counter for the for loop, and where to add the item at.
boolean stop = false;
for(i=0; stop = true; i++)
{
if(inv[i].equals("0"))
{
stop = true;
}
}
inv[i] = item;
return inv;
}
static void print(String entry){
System.out.print(entry);
}
}
And when I try and run it through the Command Prompt, I get this error:
Exception in thread "main" java.lang.NullPointerExcpetion
at mainGame.addItem(mainGame.java:113)
at mainGame.main(mainGame.java:38)

When I paste this in to a text editor, line 113 is simply a closing brace }.
However, one line before that is a logic flaw which I presume is really line 113 for you.
for(i=0; stop = true; i++)
{
if(inv[i].equals("0"))
{
stop = true;
}
}
Each iteration of the loop assigns true to stop and then tests if true equals true, which it does. Your condition to exit the loop is when true equals false, which is never the case, therefore your loop goes forever until an error occurs. Also, don't you want to iterate while stop is false? I think you have it backwards.
The next problem is your if statement, which is probably where your NullPointerException is coming from:
if(inv[i].equals("0"))
{
stop = true;
}
You assume that inv[i] refers to an object. You need a null check.
Three recommendations:
Never use = for a comparison. Use ==. Since this is a boolean, you can even simplify this to stop.
Check the length in your for loop.
Compare "0" to inv[i] instead of the other way around to avoid null pointer dereferencing.
Try this:
boolean stop = false;
for (int i = 0; i < inv.length && !stop; i++)
{
if("0".equals(inv[i])
{
stop = true;
}
}
Another option, and this is a matter of form, is to remove the looping variable and just break out of the loop explicitly.
for (int i = 0; i < inv.length; i++)
{
if("0".equals(inv[i])
{
break;
}
}

inv = new String[10]; //The player's inventory
inv[0] = "0";
inv = addItem(inv, "Blarg");//GET RID OF THIS LATER
So you only initialize one index of your array but here:
for(i=0; stop = true; i++)
{
if(inv[i].equals("0"))
{
stop = true;
}
}
.. you loop through all of them. just kidding, didn't read the full problem. You should still read the rest of my answer, but the reason why you get the NPE is because your loop condition is broken. (by the way your for loop condition is broken, it should test for equivalence using the == operator, not the assignment = operator.)
So what you actually are doing with that code is this :
inv = new String[10];
At this point you have a new String array of capacity 10, with no values inside, something like this:
[null][null][null][null][null][null][null][null][null][null]
inv[0] = "0";
Now you set [0] to "0", so:
["0"][null][null][null][null][null][null][null][null][null]
Then your loop attempts to access all of those null references, that'll probably be why you have a null reference exception.
To fix it, simply every index position in your array to anything that is not-null:
Arrays.fill(inv, "");
I use Arrays.fill() because it's shorter.

In your for loop condition, which one do you prefer?
stop = true or stop == true

for(i=0; i<inv.length && !stop; i++)
{
if(inv[i]!=null && inv[i].equals("0"))
{
stop = true;
}
}

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.