This is a later version of a Sudoku solver applet. To add a number to a square, click on it. An underline should appear in the cell. Then press 1 through 9 on your keyboard, and the number should appear in the cell. If the move isn't legal (two of the same number in the same column, for example) a notification message will appear in place of the Solve button.

Once you have clicked on the board, you can also use arrow keys to navigate between cells. To remove a number, select a cell, and use any of space, delete, backspace, or 0 to clear it.

The Solve button will make the applet attempt to solve the puzzle. In some cases, the bot will not be able to fill in all the cells. If that happens, you can continue to fill in more cells and have the bot try again. Cells that the bot fills in will be a lighter color, and you can't erase those cells.

Source code: Main applet and Cell object

Sample boards to fill in: