HOW TO PLAY
The sudoku grid consists of eighty-one squares in a nine by nine grid. To solve the sudoku, each square in the grid must contain a number between one and nine, with the following conditions:
• Each row of nine cells must contain each of the numbers from 1 to 9 once and only once.
• Each column of nine cells must contain each of the numbers from 1 to 9 once and only once.
• Each of the nine 3 by 3 boxes of nine cells must contain each of the numbers from 1 to 9 once and only once.
The sudoku starts with a partially filled grid and you must complete the grid while following the rules above. If you complete the grid, you've solved the sudoku.
Each sudoku on this site has one and only one unique solution.
Some people like to write small pencil numbers in each cell to indicate what numbers are possible in that cell. If you fill all the cells with their possible values, the answer may quickly become apparent. Particularly if some cells only have one possible value. Such cells are called an "Open Single".
USING THE SUDOKU
The rules for Sudoku can be found here.
The sudoku can be used via the mouse, the keyboard, or a combination of the two (details follow). Alternatively, you can print them out and solve them offline.
The Main Display
Above the sudoku you'll find the sudoku number and the difficulty level. To return to a sudoku at a later date, enter the sudoku number in the "More Sudoku" page.
Also above the sudoku and to the right is the timer. This shows how long (in minutes and seconds) you've been solving this sudoku. You can turn off the timer via the options menu (see below).
Below the sudoku are three buttons:
Use Pen/Use Pencil (keyboard shortcut - P)
This button is used to switch between pen and pencil input modes. You can also switch between these modes by pressing the P key on your keyboard. (See "The Sudoku" below for more information on using the pen and pencil input.)
How am I doing? (keyboard shortcut - ?)
Use this button to find if there are any errors in your current partial solution or to complete the sudoku if you think you have the full solution. If there are any errors the number of errors will be displayed and, optionally, the errors will be highlighted on the sudoku. (See the Options Menu below for how to activate this feature).
You must select this button when you have completed the sudoku (if you've filled in all the cells, the label on the button will change to "I think I've finished"). The software will then check your solution and tell you if you're correct.
Note: if at any time you select this button and errors are found in your solution you may continue to correct the errors and solve the sudoku but your mistakes will mean that this sudoku won't count towards your grading and you won't feature in any high score tables for this puzzle.
This button can also be selected by pressing the ? key on your keyboard.
Pause/Options (keyboard shortcut - esc)
Use this button to pause the timer and display the options menu. The options menu is described below. This button can also be activated by pressing the escape key on your keyboard.
The Sudoku
There are two modes for entering numbers on the sudoku grid - Pen and Pencil. See above for how to switch between these two modes.
Pen input is used to enter solutions into the grid. It allows one number per cell, as expected.
Pencil input is used to enter possible numbers in cells while working out the solution. It allows as many numbers as you wish in each square of the grid and can be very useful for working out the possible solutions.
In either mode, numbers are entered via the ring selector or the keyboard. The ring selector may be enabled or disabled via the options menu (see below).
The Ring Selector
With the ring selector enabled, clicking in a square on the sudoku grid displays a ring with all nine numbers and an X on it. Select a number to enter that number in the cell or select the X to clear all numbers from the cell.
In pen mode, the ring selector will withdraw after a number has been selected. In pencil mode, the ring selector remains to allow you to enter more numbers. If a pencil number is currently displayed, selecting the number again on the ring selector or the keyboard will remove it.
To clear the ring selector without altering the contents of the cell or after entering numbers in pencil mode, click in the sudoku anywhere outside of the ring selector.
Keyboard Input
Even with the ring selector enabled, you can enter numbers via the keyboard as follows. Click on a cell to select it. Press a number on your keyboard to enter it in the cell. Press the delete, X or 0 key to clear the cell. Press the P key to switch between pen and pencil input.
With the ring selector disabled, you can also use the arrow keys on your keyboard to select different cells.
The Options Menu
Clicking the Pause/Options button or pressing the escape key on your keyboard will stop the timer and display the options menu. To leave the options menu and return to the sudoku, click the resume button that is below the other options. The options in this menu are as follows:
Start Again
If it's all gone horribly wrong, this button will clear the grid to start again from the beginning.
Show Solution
Click this button to reveal the solution. Please note, if you reveal the solution then go on later to complete the sudoku, the sudoku will not count towards your grading.
Enable/Disable Ring Selector
Click this button to turn the ring selector on and off. With the ring selector disabled, you must use the keyboard to enter numbers and you may also use the arrow keys to select cells.
For most people, using the ring selector is the most relaxed way to solve the sudoku, but if you want to get a fast time it's usually quicker to use the keyboard with the ring selector disabled.
Show/Hide Timer
The timer will always measure and record the time it takes to solve the sudoku. But, if you're not interested in the time you can hide the timer and will never know how long the sudoku takes you. For many of us, all that matters is that we solve the sudoku.
Note, even with the timer hidden you can find out how long you took to solve the sudoku by viewing the statistics after you've solved it (see below).
Show/Hide Incorrect Cells
When you click the "How am I doing?" button, the computer tells you how many errors you've made. If there are errors, it can also show you what cells are wrong. Use this button to enable or disable this feature.
After solving the sudoku
When you've completed the grid, the button labelled "How am I doing?" will change to say "I think I've finished". Click the button to find out if you completed the sudoku correctly. If you made errors, you'll remain on the sudoku page to correct your errors.
If you are logged in and successfully completed the sudoku, the sudoku and your time to complete it will be added to your statistics. Select "My Statistics" from the main menu on any page of the site to view your statistics.
Having completed the sudoku the buttons below the sudoku display will change to three new options.
Solution/Statistics (keyboard shortcut - S)
This button reveals the solution for this solution or the statistics for this sudoku. the statistics show how many people have completed the puzzle without error and what their average time was, along with your time and how that compares to the average.