Extreme Su-Doku Help

Overview

This game of Su-doku is played on a 9x9 board of 81 cells.
The board is divided into 27 UNITS:

• Nine ROWS of 1x9 cells;
• Nine COLUMNS of 9x1 cells;
• Nine SQUARES of 3x3 cells.

Thus each UNIT (Row, Column or Square) contains nine cells

The object is to place on the board the digits 1 to 9, so that each digit occurs only once in each UNIT, and every one of the 81 cells contains a digit.

A sample completed game is shown below.

1 2 3     4 5 6     7 8 9
4 5 6     7 8 9     1 2 3
7 8 9     1 2 3     4 5 6

2 3 4     5 6 7     8 9 1
5 6 7     8 9 1     2 3 4
8 9 1     2 3 4     5 6 7

3 4 5     6 7 8     9 1 2
6 7 8     9 1 2     3 4 5
9 1 2     3 4 5     6 7 8

Each time Extreme Su-Doku is started, it will automatically restore the last game you were playing.

You may choose at any time to ask Extreme Su-Doku (via its FILE menu) to:

• Create a brand NEW game,
• OPEN previously saved game from file,
• CLEAR the board so you can enter a new game from another source (book, newspaper etc).

The origin of modern Su-Doku was the Latin Squares, a game which Euler invented in the 1780s. The 9x9 Su-Doku game is itself a 9x9 Latin Square which in turn is built up of nine smaller 3x3 Latin Squares.

Why "Extreme" Su-Doku?
To make a game easier to solve, it may contain redundant information. Extreme Su-Doku's games contain NO redundant information of this sort.

Playing the Game

Extreme Su-Doku is designed to be played without a keyboard on either:

• A PocketPC/SmartPhone using a stylus and touch screen;
• A standard PC with just the mouse.

These instructions assume you are running on a PocketPC.
The playing area consists of the 9x9 board already discribed, and a Menu bar which has:

• The digits ("1" "2" "3" "4" "5" "6" "7" "8" "9");
• The Cell Reset("_");
• And Help ("?") options.

A cell on the board is selected by taping it with the stylus. It's colour will change.
A digit on the menu bar is selected by taping it with the stylus.
Placing a digit in a cell is a two stage process:

1. Select a cell as the target cell by taping on it with the stylus till it's colour changes to Dark Blue.
2. Select the desired digit which should now appear in the target cell (at which point it's colour should change to a Light Blue).

A cell colour may be:

• Dark Blue - The single cell selected as the target cell.
• Red - The target cell if it's number duplicates another cell's number in the same Unit;
• Light Blue - Indicates the cell as been highlighted for some reason;
• White - The default colour of a cell.

An incorrectly placed digit in a cell may be replaced by either the correct digit or a blank (select Cell Reset _ on the menu bar).

• If present, sets the content of the Dark Blue target cell to blank;
• De-selects the target cell;
• Resets the colour of all cells to white;
• Resets the digits display on the Menu bar to "active".

If you get stuck, help is available via the Aids menu.

The File menu, offers several options such as the ability to restart, save and restore games.

The options available on the file menu are:

• New: Starts a new game
• Open: Selects a game from file
• Save: Saves the current game to file
• Erase: Erases a game from file
• Rerun: Re-runs the current game from scratch
• Clear: Clears the board, ready to load a game by hand
• Recalc: Re-calculates the current game's difficulty
• Print: Sends a copy of the current game to your default printer
• Exit: Save the current position and exits Extreme Su-Doku

Aids to Solving

If you get stuck, help is available via the "Aids" menu:

• Highlight: Cells with the selected number are highlighted in light blue;
• Cells: Valid blank cells for the selected number are highlighted in light blue;
• Numbers: Shows only the valid numbers (on the menu bar) for the selected cell.
• Semi-Automatic: "Solves" just one cell automatically.
• Automatic: "Solves" all the remaining cells automatically.
• Undo: Erases any digits incorrectly placed in a cell.

"Valid" does NOT imply "correct", merely that the rule against duplicate digits in a UNIT has NOT been broken.

The "Highlight" option is active by default.

The "Highlight", "Cells" and "Numbers" options are mutually exclusive.

The "Numbers" option also highlights any cells with only one valid number.

You may also highlight individual cells, with a stylus tap-and-hold or Left Mouse button click.

Extreme Su-Doku Difficulty Levels

This program initially assigns to each game a Difficulty Level.
The levels shown in the title bar are normally selected from:
Trivial, Very Simple, Simple, Easy, Moderate, Hard, Very Hard, and Fiendish.
Games up to a Moderate level can all be solved with logic, harder games may require an element of "trial and error".

Assigning a Difficulty Level to a game is a very subjective exercise. Extreme Su-Doku does it by looking at several factors, giving each a value, with the total score achieved defining the difficulty level. Some factors relate to the game's initial position; others to how Extreme Su-Doku goes about solving empty cells.

The factors relating to the initial position are:

• The number of "no choice" cells;
• If one or more UNITS are blank;
• If one of the nine digits does NOT appear;
• If some of the other given digits occur only once or twice.

The factors relating how Extreme Su-Doku solves empty cells:

• The number of different techniques, based on logic, used;
• The number of times logic fails and "Look Ahead" (brute force) is used;

Games can also be classed as:

• Solved : there are NO empty cells to solve;
• Invalid : there are NO valid solutions;
• Multiple solutions : there is NO unique solution;
• Undefined : the Difficulty Level has not been calculated.

Difficulty Level - Notes:
A clear board is classified as Undefined.
The Recalc option will re-calculate the Difficulty Level from the current position.
A valid game with more than one missing digit, must have Multiple solutions.
Extreme Su-Doku should never create an initial game with Multiple solutions.