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Applet written by Jaap Scherphuis © 2005-2017. The puzzles that this program generates can be used freely and without restrictions.
To use this program offline, save the Sudoku.jar file, by right-clicking on that link and saving it somewhere. Do the same for the current web page, saving it at the same location.

Instructions:

Generating a random puzzle: Click the 'Easy' button for an easy puzzle, or 'normal', 'hard', or 'extreme' for a more difficult one. The left side shows puzzle, right side shows solution. For a new puzzle, click the 'Clear' button, and then the 'Easy' button again.

Designing your own puzzle: Click on any cell in the left grid. The cell will be filled with a random number. Click again and it is cleared. Hold down shift and click a cell for each possible number in turn. If there is only one puzzle solution possible, it is shown on the right side. You may also click Generate to fill in more random cells to complete the puzzle problem. Any cell number that is grey is not necessary for the puzzle.

Diagonals: Select the 'Use Diagonals' box for Kokonotsu puzzles, or unselect it for standard Sudoku puzzles.

Difficulty: When there is a solution, the difficulty number is shown on the bottom right. Difficulty 1 means it can be fully solved by very simple logic. Difficulty between 2 and 9 means that slightly more complicated reasoning is needed. Difficulty 10 to 99 uses even more complex deduction rules to solve. Difficulty 100 or more means that the values of some cells have to be guessed at, or that deduction rules are needed that have not been programmed into the solver.

Log: If the 'Show Log' box is checked, a long explanation of the solution is displayed.

Symmetry: If you check the box marked '180' or '90', then the generated puzzles will have 180 or 90 degree rotational symmetry. Similarly, the boxes marked '\', '-', '/', '\' force mirror symmetry. More than one box may be checked at the same time for more symmetric patterns.

Solution Code: When there is a solution, four empty problem cells are marked with the letters A,B,C,D. The solution numbers in these cells form a code, shown on the bottom right. Players may use that code to prove they have solved the problem, without needing to send the whole puzzle and have it all checked. If you uncheck the 'Show Code' box, the code will not be shown.

Mark Excess: If this box is checked, then any numbers that are not needed will be shown in grey. If any of the grey numbers is removed the puzzle is still solvable, though it may be much harder.

Parse: The contents of the problem grid is shown on a single line. This can be copy/pasted into any other application. If you edit this line, or paste in a different puzzle, then click the parse button to update the grids. The contents of the solution grid is shown on the second line, and this can also be copy/pasted for use elsewhere.

Puzzle types: The program can generate various kinds of puzzles:
1. Sudoku: The box size is needed, 3x3 is the standard size.
2. SudokuX: Sudoku, but with the option that the diagonals also contain all symbols.
3. SudokuX Cross: A set of 5 overlapping Sudoku.
4. SudokuX Diamond: A set of 9 overlapping Sudoku.
5. Latin Square: Only rows and columns, no boxes. Note that the grid size must be given, and must be square.
6. Free Refions: A sudoku with free-form regions intead of square boxes. The sqaure grid size must be given, as well as a string denoting the regions' shapes.