CODEWITHSUNDEEP
javatail-recursionsudokubacktracking
Santanor
Santanor

Reputation: 566

Sudoku algorithm with backtracking does not return any solution

i'm a bit stuck with the Sudoku algorithm, i coded it using backtrack, and following the theorical steps this should work, and i tried to debuge it, but is too hard (and yes, it solve some numbers and does things)

i paste the code, i hope that you can help me, i really can't see where the problem is...

public void backtracking(int row,int col){
    if(row > 8){ 
        System.out.println("Solution Found!!"); 
        printSudoku(); 

    }
    if (m[row][col] != 0){
       next(row, col);
    }
    else {
        for(int i =1; i < n;i++) 
            if(row(row, i) && col(col, i)) {
                m[row][col] =i;
                next(row, col);
            }
        m[row][col] = 0;
    }


} 

public void next( int row, int col ) {
   if( col < 8)
       backtracking( row, col + 1 ) ;
   else
       backtracking( row+ 1, 0 ) ;
}

public boolean region(int x, int y, int numReg) {
    x = (x / 3) * 3 ;
    y = (y / 3) * 3 ;
    for( int r = 0; r < 3; r++ )
        for( int c = 0; c < 3; c++ )
        if( m[x+r][y+c] == numReg )
           return false ;

     return true ;
}

public boolean row(int x, int k){
    for(int i =0; i < 9; i++)
        if(m[x][i] == k)
            return false;
    return true;
}

public boolean col(int x, int k){
    for(int i =0; i < 9; i++)
        if(m[i][x] == k)
            return false;
    return true;
}

I ommited the "printSudoku" method, is just a double for and you know.

Upvotes: 0

Views: 290

Answers (1)

raffael
raffael

Reputation: 2456

The code seems almost right. As far as i can see you just forgot to call the region method. And I can't see where the variable n is coming from. Try it with this slightly modified backtracking method:

    public static void backtracking(int row, int col) {
    if (row > 8) {
        System.out.println("Solution Found!!");
        printSudoku();
        System.exit(0); //exiting after solution is found
    }
    if (m[row][col] != 0) {
        next(row, col);
    } else {
        for (int i = 1; i <= 9; i++) //replaced i < n with i<=9
            if (row(row, i) && col(col, i) && region(row, col, i)) { //calling region method too
                m[row][col] = i;
                next(row, col);
            }
        m[row][col] = 0;
    }

}

Upvotes: 1

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