Sudoku is a game of logic - the object is to complete the grid such that every row, every column, and every 3x3 block contains the digits from 1 to 9. No mathematics is required to solve the puzzles, just pure logic and reasoning.
When your cursor is on the Sudoku grid, it can be navigated in the following way:
- Ctrl + Arrows
Move around the grid
Show a pinned square
- Shift + #
Show squares with a <#>
The key choices may seem unusual, but the navigation has to avoid key presses that are reserved for the browser, for example we couldn't use CTRL+1 to highlight all squares that contain a <1> as this is opens the first window in Firefox, nor SHIFT+P as it is reserved for printing, etc.
There are six levels of difficulty, and various techniques are potentially required to solve Sudoku at each level, however, any particular Sudoku doesn't necessarily require all of the potential techniques for that level. The difficulty level is also very tricky to gauge as one person may find certain techniques easier to use than others. The hardest of one level will probably be harder than the easiest of the next level up, so there is a certain amount of crossover between the levels. Each BrainBashers Sudoku has a list of potential techniques that might be required to solve that Sudoku, some of which you might not use, as you may spot something which changes the solution path and you use other techniques.
Note: this list isn't exhaustive, these techniques are just my suggestions to help you solve BrainBashers Sudoku.
The key 'Backspace' has a reserved action, and in many browsers it acts as a 'Back' button. This may mean that your browser will go back a page, and leave the Sudoku Assistant, if you are not careful with its use. We suggest that you only use the 'Delete' key to remove digits.
- Pencil marks
You can enter more than one digit into each square. The size of the digits changes as you enter more digits in each square.
- 'Auto pencil marks'
The system can fill in the pencil marks for you automatically. Each square is checked to see what digits can possibly go there, if only one possibility remains, then that digit is filled in. You can manually change the pencil marks and run the option as many times as you like without affecting your logical deductions. For difficulties above Medium it also auto-runs until no board changes take place. When using the blank or loaded assistant for non-BrainBashers Sudoku, remember that auto-pencil marks might complete the Sudoku for you and spoil the fun, however it doesn't auto-run, so you may have to keep clicking it as the system changes the board.
- 'Show errors in red'
If this option is selected, correct digits are shown in green and incorrect ones in red. This is useful for checking your progress mid-solution. This is only available for BrainBashers Sudoku. The system only looks at squares with a single digit, and does not consider the validity of the pencil marks.
- 'Show duplicates'
If this option is selected, duplicates in a row, column or 3x3 block are shown in yellow.
- 'Show squares with a ...'
All pencil marked squares that contain the selected digit will be highlighted. This is very useful when looking for a digit which is missing from a row, column or 3x3 block.
- 'Show a pinned square'
If one of the rows, columns or 3x3 blocks contains exactly one instance of a digit, all pencil marked squares that contain this digit will be highlighted in green, with the pinned square highlighted in yellow. This is very useful for finding pinned squares. If no row, column or 3x3 block contains a pinned square, any highlights will be removed. This option requires some pencil marks on the grid.
- 'Show Potential Techniques'
This option will show you which techniques might be required to solve the current BrainBashers Sudoku.
Only BrainBashers Sudoku can be printed (the starting grid, without pencil marks).
Undo takes the Sudoku grid back to just before an auto-pencil marks was run.