Random Sodoku
@ paulspages.co.uk

(If you've arrived here direct from a search engine,
click here to see the main page)

How to play
First, get a puzzle. To generate a new, random puzzle, press 'Random Puzzle'. To get a pre-built puzzle, press 'Gallery Puzzle' (or click 'see all' to choose a puzzle from the gallery display).

You can also type the starting numbers in from another source, e.g. a puzzle in a book or newspaper. Follow the instructions in the right-hand column for typing in your own numbers.

To solve the puzzle, type numbers into the empty squares so that each horizontal row and vertical column contains the numbers 1 to 9 (i.e. with no numbers repeated). The difficult bit is that each 9-square rectangle (the areas surrounded by darker lines) must also contain the numbers 1 to 9, with no repetitions. To see an example of a completed puzzle, press 'Solve Puzzle'. 

If 'Show errors' is checked and you type an incorrect number, it will be shown in red (note - this only works with single-solution puzzles).
Tip - after typing a number, press Tab, or click elsewhere on the page, to make sure the number is checked.

Pressing 'Check my answer' will tell you whether your answers so far are correct, without revealing the rest of the puzzle.

Basic tips for solving have now been moved to the new (and expanded!) How to solve sudoku page.

Using candidate lists. A key technique in sudkou solving is writing the candidate (possible) numbers for each empty square in the corner of the square. You can do this in this page, by clicking in the top-left corner and typing the numbers in.

In manual mode it's up to you to maintain these lists, just like a printed puzzle. In automatic mode, the page calculates the lists for you, updating them whenever you solve a square. That's not 'proper' solving, of course, but is useful for practising pattern recognition.

Generating puzzles.
This page features the improved MKIII puzzle generator, with three (count 'em) ways of getting a new puzzle:

Random Puzzle. Generates a single-solution puzzle with a symmetrical layout. You can choose from 36 down to 22 starting squares. The difficulty rating of a puzzle is unknown until it's been generated, but choosing fewer squares will tend  to create harder puzzles.

This version has a new generator for puzzles with 30 or more starting squares. 30-square puzzles now range from 'easy' to outlaw rating, and are produced very quickly (mostly!).

Gallery Puzzle. This gets a pre-built puzzle (single-solution, symmetrical) from the Gallery, with your choice of difficulty level. Click 'see all' to view the Gallery menu, and choose a puzzle to solve.

Non-symmetric puzzle. This generates a single-solution puzzle with your choice of difficulty level. The layout will be non-symmetrical.

To be solvable entirely by logic (no guesses), a puzzle must have only one possible solution. All puzzles generated by this page (including Gallery puzls) are single-solution. The page will warn you if a puzzle you've typed in or imported has more than one solution. 

Please note - puzzles rated 'outlaw' by this page may still require a guess, even though they have just one solution. All other puzzles generated by this page's 'Random Puzzle' button are guaranteed to be solvable by logic alone.

Have fun!

Tip: Use Firefox to view the solver - it shows the numbers as they're being calculated.

Tip #2: Press Tab after you type each number (or just click somewhere else on the page) - this will check your data, and update auto candidate lists if you're using them.

Tip #3: When importing and solving really tough puzzles, your browser may show 'Script running slowly' messages. Choose 'No' (IE) or 'Cancel' (Firefox) to let the solver keep on running. It'll get there in the end!

Sudoku.com. The 'official' sudoku site - puzzles, tips, links.

The Daily Sudoku. A new puzzle every day, plus lots of links.

Daily Telegraph Sudoku. Puzzles and links, plus an excellent guide to solving techniques.

Sudoku Solver. This Excel-based solver gave me the idea for the solver in this page - thanks!

Mark Huckvale's Sudoku Workpad. Puzzle generator and solver.

How the solver in this page works for anyone who's interested.

Switching symbols?
The big secret about sudoku is that it isn't really a number puzzle at all (it's about logic). The characters 1 to 9 are a convenient set of symbols that we all recognise, but they have no mathematical significance in this context.
Sudoku works just as well using shapes, colours - even vegetables ('each row must contain a carrot, onion, potato...."). Any set of nine distinct entities will do.
We can't stretch to vegetables here at paulspages, but we can manage a couple of alternative symbol sets. The alphabetical ones are fairly easy, but the punctuation symbols are harder, mainly because we don't have a pre-conceived order for them (unlike 'ABC..'), so it's harder to work methodically through them.
To switch symbol sets, just select a different set from the drop-down list. You can do this at any time, without losing the current puzzle. (Note: manual candidate lists won't be converted - sorry!)
Alternative symbol sets also work on the printer page, and import/export.
Go on - try it if you're tough enough!