Develop Reference

Game of life Oscillators and Spaceships not working

Hi so I am currently working on a game of life with javafx canvas. However there seems to be a bug in my algorithm. The still lifes are working however the rest is not, the patterns like the glider aren't moving the way they should. Im using a 2d int array, ALIVE is 1 and DEAD is 0. Here is my algorithm:
private void checkRules() {
int[][] newBoard = board;
int amountOfAliveNeighbours;
for (int y = 0; y < board.length; y++) {
for (int x = 0; x < board[y].length; x++) {
amountOfAliveNeighbours = getAmountOfAliveNeighbours(x, y);
if (board[y][x] == ALIVE) {
if (amountOfAliveNeighbours == 2 || amountOfAliveNeighbours == 3) {
newBoard[y][x] = ALIVE;
}else{
newBoard[y][x] = DEAD;
}
} else if (board[y][x] == DEAD){
if (amountOfAliveNeighbours == 3) {
newBoard[y][x] = ALIVE;
}else{
newBoard[y][x] = DEAD;
}
}
}
}
board = newBoard;
}
private int getAmountOfAliveNeighbours(int x, int y) {
int neighbours = 0;
// top left
if (x - 1 >= 0 && y - 1 >= 0) {
if (board[y - 1][x - 1] == ALIVE)
neighbours++;
}
// top center
if (y - 1 >= 0) {
if (board[y - 1][x] == ALIVE)
neighbours++;
}
// top right
if (x + 1 < board[0].length && y - 1 >= 0) {
if (board[y - 1][x + 1] == ALIVE)
neighbours++;
}
// middle left
if (x - 1 >= 0) {
if (board[y][x - 1] == ALIVE)
neighbours++;
}
// middle right
if (x + 1 < board[0].length) {
if (board[y][x + 1] == ALIVE)
neighbours++;
}
// bottom left
if (x - 1 >= 0 && y + 1 < board.length) {
if (board[y + 1][x - 1] == ALIVE)
neighbours++;
}
// bottom center
if (y + 1 < board.length) {
if (board[y + 1][x] == ALIVE)
neighbours++;
}
// bottom right
if (x + 1 < board[0].length && y + 1 < board.length) {
if (board[y + 1][x + 1] == ALIVE)
neighbours++;
}
return neighbours;
}

Allocate the memory for the temporary board like this:
int[][] newBoard = new int[board.length][board[0].length];
I would suggest to refactor calculation of neighbours:
private int getAmountOfAliveNeighbours(int x, int y) {
int neighbours = 0;
for (int dx = -1; dx <= 1; dx++) {
for (int dy = -1; dy <= 1; dy++) {
if ((dx !=0 || dy != 0) && isAlive(x + dx, y + dy)) {
neighbours++;
}
}
}
return neighbours;
}
private boolean isAlive(int x, int y) {
return (x >= 0) && (x < board.length) &&
(y >= 0) && (y < board[0].length) &&
(board[x][y] == ALIVE);
}

Stack Overflow Error in a Self Calling Function in Java (Number of Islands)

I did some research on what causes a stack overflow errors, and I can conclude it is being caused by a recursive function in a program that is supposed to "count the number of islands" in an array. I understand what is causing the issue, but not sure why this is happening, or my main question is what to actually do about it. I found that if I slow down the program by having it repeatedly printing out something to the console, it works, but it takes forever to complete. Is there a way I can keep the program speed without the error, or a better way to solve the problem (search up "number of islands" to find the problem). Also, the array is two dimensional with a size of 1050 by 800.
public class NumOfIslands {
static boolean[][] dotMap = new boolean[1050][800];
static boolean visited[][] = new boolean[1050][800];
static int total = 0;
public static void main(String args[]) {
defineArrays();
run();
}
public static void findObjects(int xCord, int yCord) {
for(int y = yCord - 1; y <= yCord + 1; y++) {
for(int x = xCord - 1; x <= xCord + 1; x++) {
if(x > -1 && y > -1 && x < dotMap[0].length && y < dotMap.length) {
if((x != xCord || y != yCord) && dotMap[x][y] == true && visited[x][y] != true) {
visited[x][y] = true;
findObjects(x,y);
//System.out.println("test");
}
}
}
}
}
public static void defineArrays() {
for(int y = 0; y < 800; y++) {
for(int x = 0; x < 1050; x++) {
dotMap[x][y] = true;
}
}
}
public static int run() {
//dotMap = DisplayImage.isYellow;
System.out.println(dotMap.length + " " + dotMap[0].length);
int objects = 0;
for(int y = 439; y < 560/*dotMap[0].length*/; y++) {
for(int x = 70; x < 300/*dotMap.length*/; x++) {
if(dotMap[x][y] == true && visited[x][y] != true) {
visited[x][y] = true;
objects++;
findObjects(x,y);
}
}
}
System.out.println("total" + total);
System.out.println(objects);
return objects;
}
}

StackOverflowError reasons. In your example each call to findObjects adds 2 variables to the stack int x and int y from loops.
One of the fastest solution:
class Solution {
int m, n;
public int numIslands(char[][] grid) {
if (grid == null || grid.length == 0) {
return 0;
}
m = grid.length;
n = grid[0].length;
int counter = 0;
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
if (grid[i][j] == '1') {
visit(grid, i, j);
counter++;
}
}
}
return counter;
}
public void visit(char[][] grid, int i, int j) {
if (i < 0 || i >= m || j < 0 || j >= n) {
return;
}
if (grid[i][j] == '0') {
return;
}
grid[i][j] = '0';
visit(grid, i - 1, j);
visit(grid, i + 1, j);
visit(grid, i, j - 1);
visit(grid, i, j + 1);
}
}
All recursive algorithms can be implemented with loops. One of the example is below. The Solution implements BFS (Breadth-first search) algorithm, more details on wikipedia.
class Solution {
public int numIslands(char[][] grid) {
if (grid == null || grid.length == 0) {
return 0;
}
int nr = grid.length;
int nc = grid[0].length;
int num_islands = 0;
for (int r = 0; r < nr; ++r) {
for (int c = 0; c < nc; ++c) {
if (grid[r][c] == '1') {
++num_islands;
grid[r][c] = '0'; // mark as visited
Queue<Integer> neighbors = new LinkedList<>();
neighbors.add(r * nc + c);
while (!neighbors.isEmpty()) {
int id = neighbors.remove();
int row = id / nc;
int col = id % nc;
if (row - 1 >= 0 && grid[row-1][col] == '1') {
neighbors.add((row-1) * nc + col);
grid[row-1][col] = '0';
}
if (row + 1 < nr && grid[row+1][col] == '1') {
neighbors.add((row+1) * nc + col);
grid[row+1][col] = '0';
}
if (col - 1 >= 0 && grid[row][col-1] == '1') {
neighbors.add(row * nc + col-1);
grid[row][col-1] = '0';
}
if (col + 1 < nc && grid[row][col+1] == '1') {
neighbors.add(row * nc + col+1);
grid[row][col+1] = '0';
}
}
}
}
}
return num_islands;
}
}

the problem is in this function
public static void findObjects(int xCord, int yCord) {
for(int y = yCord - 1; y <= yCord + 1; y++) {
for(int x = xCord - 1; x <= xCord + 1; x++) {
if(x > -1 && y > -1 && x < dotMap[0].length && y < dotMap.length) {
if((x != xCord || y != yCord) && dotMap[x][y] == true && visited[x][y] != true) {
visited[x][y] = true;
findObjects(x,y);
//System.out.println("test");
}
}
}
}
}`
at here you are builiding a stack of recursive calls to findobjects and ultimately it has no termination condition so it ends up at infinite stacks of findobjects, so my solution is if you are just checking that if x and y varaibles are not equal and visited[x][y] is not true then there is no need to call for recursion just comment the recursive call, because your loop already do what you want the recursive call to do.
public static void findObjects(int xCord, int yCord) {
for(int y = yCord - 1; y <= yCord + 1; y++) {
for(int x = xCord - 1; x <= xCord + 1; x++) {
if(x > -1 && y > -1 && x < dotMap[0].length && y < dotMap.length) {
if((x != xCord || y != yCord) && dotMap[x][y] == true && visited[x][y] != true) {
visited[x][y] = true;
//findObjects(x,y);
//System.out.println("test");
}
}
}
}
}

Java: Tic-Tac-Toe - How To AVOID Repeated Cell From Being Input By User?

How do I prevent the same tic tac toe coordinate from being inputted by the user?
The user input is taken at the main method in the Game Class.
The tic tac toe cells with [x, y] coordinates ranging from (0-2) can be either:
0(_), 1 (X) or 2 (O)
Grid Class with alpha beta search tree pruning algorithm
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
class Grid {
List<Cell> availableCells;
int[][] board = new int[3][3];
Scanner scan = new Scanner(System.in);
// Set limit to search tree depth
int treeDepth = 9;
List<CellsAndScores> rootsChildrenScore = new ArrayList<>();
public int score() {
int score = 0;
// Check all columns
for (int j = 0; j < 3; ++j) {
int X = 0;
int O = 0;
for (int i = 0; i < 3; ++i) {
if (board[i][j] == 0) {
} else if (board[i][j] == 1) {
X++;
} else {
O++;
}
}
score += changeInScore(X, O);
}
// Check all rows
for (int i = 0; i < 3; ++i) {
int X = 0;
int O = 0;
for (int j = 0; j < 3; ++j) {
if (board[i][j] == 0) {
} else if (board[i][j] == 1) {
X++;
} else {
O++;
}
}
score += changeInScore(X, O);
}
int X = 0;
int O = 0;
// Check diagonal (first)
for (int i = 0, j = 0; i < 3; ++i, ++j) {
if (board[i][j] == 1) {
X++;
} else if (board[i][j] == 2) {
O++;
} else {
}
}
score += changeInScore(X, O);
X = 0;
O = 0;
// Check Diagonal (Second)
for (int i = 2, j = 0; i > -1; --i, ++j) {
if (board[i][j] == 1) {
X++;
} else if (board[i][j] == 2) {
O++;
} else {
}
}
score += changeInScore(X, O);
return score;
}
private int changeInScore(int X, int O) {
int change;
if (X == 3) {
change = 100;
} else if (X == 2 && O == 0) {
change = 10;
} else if (X == 1 && O == 0) {
change = 1;
} else if (O == 3) {
change = -100;
} else if (O == 2 && X == 0) {
change = -10;
} else if (O == 1 && X == 0) {
change = -1;
} else {
change = 0;
}
return change;
}
public int alphaBetaMinimax(int alpha, int beta, int depth, int turn) {
if (beta <= alpha) {
System.out.println("Pruning at tree depth = " + depth + " alpha: " + alpha + " beta: " + beta);
if (turn == 1)
return Integer.MAX_VALUE;
else
return Integer.MIN_VALUE;
}
if (depth == treeDepth || gameOver()) {
return score();
}
List<Cell> cellsAvailable = getAvailableStates();
if (cellsAvailable.isEmpty()) {
return 0;
}
if (depth == 0) {
rootsChildrenScore.clear();
}
int maxValue = Integer.MIN_VALUE, minValue = Integer.MAX_VALUE;
for (int i = 0; i < cellsAvailable.size(); ++i) {
Cell cell = cellsAvailable.get(i);
int currentScore = 0;
if (turn == 1) {
placeAMove(cell, 1);
currentScore = alphaBetaMinimax(alpha, beta, depth + 1, 2);
maxValue = Math.max(maxValue, currentScore);
// Set alpha
alpha = Math.max(currentScore, alpha);
if (depth == 0) {
rootsChildrenScore.add(new CellsAndScores(currentScore, cell));
}
} else if (turn == 2) {
placeAMove(cell, 2);
currentScore = alphaBetaMinimax(alpha, beta, depth + 1, 1);
minValue = Math.min(minValue, currentScore);
// Set beta
beta = Math.min(currentScore, beta);
}
// reset board
board[cell.x][cell.y] = 0;
// Do not evaluate the rest of the branches after search tree is pruned
if (currentScore == Integer.MAX_VALUE || currentScore == Integer.MIN_VALUE)
break;
}
return turn == 1 ? maxValue : minValue;
}
public boolean gameOver() {
// Game is over is someone has won, or board is full (draw)
return (hasXWon() || hasOWon() || getAvailableStates().isEmpty());
}
public boolean hasXWon() {
if ((board[0][0] == board[1][1] && board[0][0] == board[2][2] && board[0][0] == 1)
|| (board[0][2] == board[1][1] && board[0][2] == board[2][0] && board[0][2] == 1)) {
// System.out.println("X Diagonal Win");
return true;
}
for (int i = 0; i < 3; ++i) {
if (((board[i][0] == board[i][1] && board[i][0] == board[i][2] && board[i][0] == 1)
|| (board[0][i] == board[1][i] && board[0][i] == board[2][i] && board[0][i] == 1))) {
// System.out.println("X Row or Column win");
return true;
}
}
return false;
}
public boolean hasOWon() {
if ((board[0][0] == board[1][1] && board[0][0] == board[2][2] && board[0][0] == 2)
|| (board[0][2] == board[1][1] && board[0][2] == board[2][0] && board[0][2] == 2)) {
// System.out.println("O Diagonal Win");
return true;
}
for (int i = 0; i < 3; ++i) {
if ((board[i][0] == board[i][1] && board[i][0] == board[i][2] && board[i][0] == 2)
|| (board[0][i] == board[1][i] && board[0][i] == board[2][i] && board[0][i] == 2)) {
// System.out.println("O Row or Column win");
return true;
}
}
return false;
}
public List<Cell> getAvailableStates() {
availableCells = new ArrayList<>();
for (int i = 0; i < 3; ++i) {
for (int j = 0; j < 3; ++j) {
if (board[i][j] == 0) {
availableCells.add(new Cell(i, j));
}
}
}
return availableCells;
}
public void placeAMove(Cell Cell, int player) {
board[Cell.x][Cell.y] = player; // player = 1 for X, 2 for O
}
public Cell returnBestMove() {
int MAX = -100000;
int best = -1;
for (int i = 0; i < rootsChildrenScore.size(); ++i) {
if (MAX < rootsChildrenScore.get(i).score) {
MAX = rootsChildrenScore.get(i).score;
best = i;
}
}
return rootsChildrenScore.get(best).cell;
}
public void displayBoard() {
System.out.println();
for (int i = 0; i < 3; ++i) {
for (int j = 0; j < 3; ++j) {
if (board[i][j] == 0)
System.out.print("_" + " ");
if (board[i][j] == 1)
System.out.print("X" + " ");
if (board[i][j] == 2)
System.out.print("O" + " ");
}
System.out.println("");
}
System.out.println();
}
public void resetGrid() {
for (int i = 0; i < 3; ++i) {
for (int j = 0; j < 3; ++j) {
board[i][j] = 0;
}
}
}
}
Cell class
class Cell {
int x, y;
public Cell(int x, int y) {
this.x = x;
this.y = y;
}
public String toString() {
return "[" + x + ", " + y + "]";
}
}
class CellsAndScores {
int score;
Cell cell;
CellsAndScores(int score, Cell cell) {
this.score = score;
this.cell = cell;
}
}
Game Class with main method - takes user input
import java.util.Random;
public class Game {
public static void main(String[] args) {
Grid grid = new Grid();
Random random = new Random();
grid.displayBoard();
System.out.print("Who moves first? [1]Computer(X) [2]User(O): ");
int turn = grid.scan.nextInt();
if (turn == 1) {
Cell p = new Cell(random.nextInt(3), random.nextInt(3));
grid.placeAMove(p, 1);
grid.displayBoard();
}
while (!grid.gameOver()) {
int x = 0, y = 0;
System.out.print("Please enter an x coordinate [0-2]: ");
x = grid.scan.nextInt();
System.out.print("Please enter an y coordinate [0-2]: ");
y = grid.scan.nextInt();
Cell userMove = new Cell(y, x);
grid.placeAMove(userMove, 2); // 2 for O and O is the user
grid.displayBoard();
if (grid.gameOver())
break;
grid.alphaBetaMinimax(Integer.MIN_VALUE, Integer.MAX_VALUE, 0, 1);
for (CellsAndScores pas : grid.rootsChildrenScore)
System.out.println("Cell: " + pas.cell + " Score: " + pas.score);
grid.placeAMove(grid.returnBestMove(), 1);
grid.displayBoard();
}
if (grid.hasXWon()) {
System.out.println("Unfortunately, you lost!");
grid.resetGrid();
} else if (grid.hasOWon()) {
System.out.println("You win!");
grid.resetGrid();
} else {
System.out.println("It's a draw!");
grid.resetGrid();
}
}
}

My answer would be to add a boolean check method into your Grid.java class and then in your main method - call this boolean check method before the placeAMove() method.
For example, in your Grid.java class, adding the following method:
/*
* Return true if space is ok to use.
*/
public boolean isMoveOK(Cell cell) {
return board[cell.x][cell.y] == 0;
}
This way, using your pre-existing 0/1/2 values that keep track of empty/X/O space values, you may provide a check to see if the space value is zero or not.
This would be one way to use it in your main method, to answer your question of, 'How do I prevent the same tic tac toe coordinate from being inputted by the user?'
Cell userMove = new Cell(y, x);
if (grid.isMoveOK(userMove)) {
grid.placeAMove(userMove, 2); // 2 for O and O is the user
} else {
System.out.println("Please try a different space/cell");
continue;
}
grid.displayBoard();
if (grid.gameOver())
break;
In this way, I am skipping the remaining loop code in your main method loop, until there's a valid open space. (When there is, then the program should proceed to check for winning values or whether to proceed playing)
Hope this answers your question! :)
Cheers

Reversi (Othello) Java simple program returns wrong moves

I've been trying to implement simple program that returns valid move of Reversi / Othello game.
Unfortunately, it doesn't work and I cannot really see why. It returns [2,2] which is certainly not valid move.
//myColor, opponentColor, Reversi move etc. are already defined.
I would be glad if you pointed out flaw in my system.
#Override
public ReversiMove makeNextMove(int[][] board) {
for (int y = 0; y < 8; y++) {
for (int x = 0; x < 8; x++) {
if (board[y][x] != myColor && board[y][x] != opponentColor) {
int nextX = x + 1;
while (nextX < 7 && board[y][nextX] == this.opponentColor) {
if (board[y][nextX + 1] == this.myColor) {
return new ReversiMove(y,x);
}
nextX++;
}
nextX = x - 1;
while (nextX > 0 && board[y][nextX] == this.opponentColor) {
if (board[y][nextX - 1] == this.myColor) {
return new ReversiMove(y,x);
}
nextX--;
}
int nextY = y + 1;
while (nextY < 7 && board[nextY][x] == this.opponentColor) {
if (board[nextY + 1][x] == this.myColor) {
return new ReversiMove(y,x);
}
nextY++;
}
nextY = y - 1;
while (nextY > 0 && board[nextY][x] == this.opponentColor) {
if (board[nextY - 1][x] == this.myColor) {
return new ReversiMove(y,x);
}
nextY--;
}
nextX = x + 1;
nextY = y + 1;
while (nextX < 7 && nextY < 7 && board[nextY][nextX] == this.opponentColor) {
if (board[nextY + 1][nextX + 1] == this.myColor) {
return new ReversiMove(y,x);
}
nextX++;
nextY++;
}
nextX = x - 1;
nextY = y - 1;
while (nextX > 0 && nextY > 0 && board[nextY][nextX] == this.opponentColor) {
if (board[nextY - 1][nextX - 1] == this.myColor) {
return new ReversiMove(y,x);
}
nextX--;
nextY--;
}
nextX = x + 1;
nextY = y - 1;
while (nextX < 7 && nextY > 0 && board[nextY][nextX] == this.opponentColor) {
if (board[nextY - 1][nextX + 1] == this.myColor) {
return new ReversiMove(y,x);
}
nextX++;
nextY--;
}
nextX = x - 1;
nextY = y + 1;
while (nextX > 0 && nextY < 7 && board[nextY][nextX] == this.opponentColor) {
if (board[nextY + 1][nextX - 1] == this.myColor) {
return new ReversiMove(y,x);
}
nextX--;
nextY++;
}
}
}
}
return new ReversiMove(-1, -1);
}
}

board[x][y] structure...
sometime refer as:
board[y][nextX] instead of board[nextX][y]

Efficient way to find how many neighbouring elements with a specific value there are around a particular element in an array

If I have a 2D int array called myArray that is for example 3x3 size and its elements can only have either 1 or 0 for values, what would be an efficient way to calculate how many 1s there are around a particular element? E.g:
[0][0][0]
[0][1][0]
[1][1][1]
The element myArray[0][0] would have neighbourCount of 1 while myArray[0][1] would have a neighbourCount of 3.
This is my current brute force code. myArray = currentGeneration
public int neighbours(int x, int y) { //x and y are 0 index based coordinates, they are swapped inside to corespond with actual x and y coordinates
int neighbourCounter = 0;
if(x == 0 && y == 0) {
if(currentGeneration[y+1][x] == 1) {
neighbourCounter++;
}
if(currentGeneration[y][x+1] == 1) {
neighbourCounter++;
}
if(currentGeneration[y+1][x+1] == 1) {
neighbourCounter++;
}
} else if(x == 0 && y == currentGeneration.length - 1) {
if(currentGeneration[y-1][x] == 1) {
neighbourCounter++;
}
if(currentGeneration[y][x+1] == 1) {
neighbourCounter++;
}
if(currentGeneration[y-1][x+1] == 1) {
neighbourCounter++;
}
} else if(x == currentGeneration[0].length - 1 && y == currentGeneration.length - 1) {
if(currentGeneration[y-1][x] == 1) {
neighbourCounter++;
}
if(currentGeneration[y][x-1] == 1) {
neighbourCounter++;
}
if(currentGeneration[y-1][x-1] == 1) {
neighbourCounter++;
}
} else if( y == 0 && x == currentGeneration[0].length - 1) {
if(currentGeneration[y][x-1] == 1) {
neighbourCounter++;
}
if(currentGeneration[y+1][x] == 1) {
neighbourCounter++;
}
if(currentGeneration[y+1][x-1] == 1) {
neighbourCounter++;
}
} else if(y == 0) {
for(int i = -1; i <= 1; i+=2) {
if(currentGeneration[y][x+i] == 1) {
neighbourCounter++;
}
}
if(currentGeneration[y+1][x] == 1) {
neighbourCounter++;
}
for(int i = -1; i <= 1; i+=2) {
if(currentGeneration[y+1][x+i] == 1) {
neighbourCounter++;
}
}
} else if(x == 0) {
for(int i = -1; i <= 1; i+=2) {
if(currentGeneration[y+i][x] == 1) {
neighbourCounter++;
}
}
if(currentGeneration[y][x+1] == 1) {
neighbourCounter++;
}
for(int i = -1; i <= 1; i+=2) {
if(currentGeneration[y+i][x+1] == 1) {
neighbourCounter++;
}
}
} else if(y == currentGeneration.length - 1) {
for(int i = -1; i <= 1; i+=2) {
if(currentGeneration[y][x+i] == 1) {
neighbourCounter++;
}
}
if(currentGeneration[y-1][x] == 1) {
neighbourCounter++;
}
for(int i = -1; i <= 1; i+=2) {
if(currentGeneration[y-1][x+i] == 1) {
neighbourCounter++;
}
}
} else if(x == currentGeneration[0].length - 1) {
for(int i = -1; i <= 2; i+=2) {
if(currentGeneration[y+i][x] == 1) {
neighbourCounter++;
}
}
if(currentGeneration[y][x-1] == 1) {
neighbourCounter++;
}
for(int i = -1; i <= 2; i+=2) {
if(currentGeneration[y+i][x-1] == 1) {
neighbourCounter++;
}
}
} else {
for(int i = -1; i <= 1; i+=2) {
if(currentGeneration[y+i][x] == 1) {
neighbourCounter++;
}
if(currentGeneration[y][x+i] == 1) {
neighbourCounter++;
}
if(currentGeneration[y+i][x+i] == 1) {
neighbourCounter++;
}
if(currentGeneration[y+i][x-i] == 1) {
neighbourCounter++;
}
}
}
return neighbourCounter;
}

How about that:
public static int findNeighbors(int x, int y, int[][] a) {
int sum = 0;
for ( int i = (y>0 ? y-1 : 0); i <= (y<a.length-1 ? y+1 : a.length-1); ++i )
for ( int j = (x>0 ? x-1 : 0); j <= (x<a[0].length-1 ? x+1 : a[0].length-1); ++j )
sum += a[i][j];
sum -= a[y][x];
return sum;
}