Java - creating sudoku - tips?

Ideally, your game board should be represented by a 9x9 two dimensional array, probably of integers. A second grid should contain the initial game state so the user doesn't overwrite squares that they shouldn't. You can then use zero to represent blank squares.

This should simplify things by allowing you to loop when checking for win rows/columns.

The 3x3 squares can still be handled by nested loops.

For example:

int checkBox(int [][] grid, int bX, int bY) {

  int ret = 0; // Return 0 for a correctly filled box. 1 for a blank square. 2 for two or more squares containing the same number, i.e. illegal input. 3 for both an empty square and illegal input.

  int bits = 0; // Use bits 1 - 9 to represent each number used

  for (int x = 3 * bX; x < 3 * (bX + 1); ++x) {

    for (int y = 3 * bY; y < 3 * (bY + 1); ++y) {

      int val = grid[y][x]; // Assuming it uses a grid[row][column] setup

      if (val == 0)

        ret |= 1; // There's a blank square

      else if (bits & (1 << val))

        ret |= 2; // The user used the same number twice

      else

        bits |= 1 << val;

    }

  }

  return ret;

}

Undo/Redo can be handled using a stack of small objects representing the users actions. Each time the player makes a move, push the move onto the undo stack. Clear the redo stack if not empty. On undo, pop the undo stack, use the information in the object to undo the last move, and push it onto the redo stack. On redo, pop the redo stack, use the information in the object to redo the undone move and push it onto the undo stack.

If you haven't encountered stacks yet, think of a stack of plates. You can only add/remove things from the top. That's basically how stack objects work. Traditionally, removing an item is called popping the stack and adding an item is pushing the item onto the stack.

In Sudoku, there isn't really a game lost state - the closest you get is the user filling the table with incorrect numbers, which can be cleared/undone. If you use similar checkRow() and checkColumn() methods to my checkBox() method above, loop through every row, column and box, OR all the results together and if you get an answer of 2, it meant that game has no empty squares and there are rows/columns/boxes which have the same digit used twice. If it's 1 or 3, there are empty squares left. If it's 0, the input is good and the user won.

The only time an unwinnable state can occur is if it's unwinnable from the very beginning, i.e. the starting data is bad.

How do you want to find out that somebody wants to write to a certain cell? (In forms you could place text controls)

In a console application you need to work with querying the cursor.

Checking: you need to perform three checks:

1. check whether there are unique numbers in the horizontal row

2. as 1. for the vertical column

3. nine square box.

The check is always the same: if there is a repetition of numbers (i.e. 2 times 3) then you have an error and have to delete/mark the last entry.

Tips... okay 1) CALM DOWN. 2) If you cant solve it, throw it away. Try again later. 3) When you get back, continue reading the tips. 4) Look for numbers in a horizontal and vertical ways. 5) Look for numbers in 9-box boxes. 6) Take pictures and post it up so someone can solve them for you. 7) Don't give up. 8) Never ever give up. 9) Don't listen to me. 10) Disregard rule 9.

Need more info to answer

I was wondering the same thing too today