Sudoku

[Akole]

...

[destin]

If you want to return the answer of a specified square, then you're going to need to solve it first. I would recommend having a class Square, which would hold all the possible values of that square.
The board would be a 9 by 9 array of these squares.

class Square {
    ArrayList<Integer> possibilities = new ArrayList<Integer>();
    
    public Square() {
        for (int i = 1; i <= 9; i++) {
            possibilities.add(i);
        }
    }
    
    /** this will be called only for the squares that are given to us */
    public Square(int num) {
        if (num => 1 && num <= 9) {
            possibilities.add(num);
        } 
    }
    
    public void removePossibility(int num) {
        possibilities.remove(num);
    }
}

etc.

About the algorithm, you're going to have to come up with that yourself. For example, if you have a number 4 given to you at index (1, 0), then you'll have to do something like:

for (int i = 0; i < 9; i++) {
    if (i != 0) {
        square[1][i].remove(4);
    }
    if (i != 1) {
        square[i][0].remove(4);
    }
}

for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 3; j++) {
        if (i != 1 and j != 0) {
            square[i][j].remove(4);
        }
    }
}

Good luck!

[major]

ArrayList<Integer> possibilities = new ArrayList<Integer>();

Implemented as of java 1.5, from what i have read (I think)