The oku grid consists of eighty-one squares in a nine by nine grid.
To solve the doku, 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".
For a guide on playing our sudoku view the user guide below.
The rules for Sudoku can be found in the upper section "How
to Play".
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:
Print Sudoku
Click this button to print out the sudoku in its current state
so you can complete it later using pen and paper. If you do
solve the sudoku, you may wish to keep your solution for
entering later to improve your grading - just select the sudoku
by entering its number on the select sudoku page.
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.
Instructions
Click this button to read these instructions without
interrupting your game.
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.
Try Another Sudoku (keyboard shortcut - N)
Click this button to try another sudoku of the same difficulty
as the one you just completed.
Try A Different Sudoku (keyboard shortcut - O)
Click this button to try another sudoku of a different
difficulty to the one you just completed.
