How to Generate a -complete- sudoku board? algorithm error

Question

I\'m trying to generate a complete (ie, each cell filled with a number) Sudoku-like board. It\'s for something else that has nothing to do with sudokus, so I am not interest

Answer 1

Your problem is you are using Strings. Try a recursive algorithm using integers. This algorithm will be useful for a sudoku of any size. While choosing random numbers within each call does work, it'll take much longer. If you choose a set of random numbers to go through if the next cell doesnt work, then you will not use the same number again. This algorithm will create a unique puzzle every time.

public class Sudoku {
    //box size, and game SIZE ==> e.g. size = 3, SIZE = 9
    //game will be the game
    private int size, SIZE;
    private int[][] game;

    public Sudoku(int _size) {
        size = _size;
        SIZE = size*size;
        game = generateGame();
    }

    //This will return the game
    private int[][] generateGame() {
        //Set everything to -1 so that it cannot be a value
        int[][] g = new int[SIZE][SIZE];
        for(int i = 0; i < SIZE; i++)
            for(int j = 0; j < SIZE; j++)
                g[i][j] = -1;

        if(createGame(0, 0, g))
            return g;
        return null;
    }

    //Create the game
    private boolean createGame(int x, int y, int[][] g) {
        //An array of integers
        Rand r = new Rand(SIZE);

        //for every random num in r
        for(int NUM = 0; NUM < size; NUM++) {
            int num = r.get(NUM);

            //if num is valid
            if(isValid(x, y, g, num)) {
                //next cell coordinates
                int nx = (x+1)%SIZE, ny = y;
                if(nx == 0) ny++;

                //set this cell to num
                g[x][y] = num;

                //if the next cell is valid return true
                if(createGame(nx, ny, g)) return true;

                //otherwise return false
                g[x][y] = -1;
                return false;
            }
        }
        return false;
    }

    private boolean isValid(int x, int y, int[][] g, int num) {
        //Rows&&Cols
        for(int i = 0; i < SIZE; i++)
            if(g[i][y] == num || g[x][i] == num) return false;
        //Box
        int bx = x - x%size;, by = y - y%size;
        for(int i = bx; i < bx + size; i++) {
            for(int j = by; j < by + size; j++) {
                if(g[i][j] == num)return false;
            }
        }
        return true;
    }
}

public class Rand {
    private int rSize;
    private int[] r; 
    public Rand(int _size) {
        rSize = _size;
        r = new int[size];
        for(int i = 0; i < rSize; r++)r[i] = i;
        for(int i = 0; i < rSize*5; r++) {
            int a = (int)(Math.random()*rSize);
            int b = (int)(Math.random()*rSize);
            int n = r[a];
            r[a] = r[b];
            r[b] = n;
    }
    public void get(int i) {
        if(i >= 0 && i < rSize) return r[i]; return -1;
    } 
}