This instructable provides step by step instructions to complete a Sudoku puzzle by simple process of elimination.

One of the things I that drove me crazy about Sudoku is how difficult it is to return to a puzzle if you get interupted. This system allows you to walk away from a puzzle at any time and return exactly where you left off.
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Step 1: What you need to begin

You need:

1. A sudoku puzzle. I enlarged this one (which was the puzzle that appeared on on July 8, 2006.) to make photography easier. I find this system works better on larger puzzles.

2. A pencil, Not a pen. A pencil.

3. An eraser.

Step 2: Fill in the "Missing Grid"

You see, a Sudoku puzzle is missing a grid. Once you put in this grid, it is sooo much easier.

Enter the numbers 1 through 9 in a "tic-tac-toe" pattern in every blank box.

Step 3: Erase "Across"

For each number that is preprinted in the puzzle, you will start erasing that number from the appropriate grids you just wrote in.

So the first number (in the upper right corner) is a "6". Erase every other "6" in that row. Once you have completed the erasing, draw a line across the top of the number to indicate that you have cleared out that line.

Step 4: Erase Down

Now, for that same number "6", erase the corresponding "6"'s in every box in the same column. Once you have completed erasing, draw a line down the edge of the number to indicate that you have completed this step.

Step 5: Erase "All Around"

Ok, last step for the first number "6" Erase all the "6"s in the same quadrant. Then draw a circle around the number to indicate you have completed this step.

Now you have eliminated all the sixes from all the other blocks. That indicates that a Six canot appear in any of those blocks.

Keep going, repeat those same three steps for all the other pre-printed numbers in the puzzle.
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hagaizenberg made it!1 month ago

There are a few simple techniques to solve Sudoku and they are:

Last Digit -

Hidden Singles -

and Naked Singles -

You also need to understand what boxes are (see image below)

DougP41 month ago

I used dots for about a year and eventually gave it up. Not sure why anymore. I think the dots are more common in Europe. My personal challenge now is to do my solving with no jots whatsoever. I have worked my way up to the Nikoli X-treme book this way. I have to revert to jots about half the time in that book.

VickiGene1 month ago

Am I the only person who uses a "dot" system instead of numbers? The dots are so much easier to fit into the puzzle and easy to recognize. There are 9 squares. The squares on the left are 1,4,7; middle, 2,5,8; right, 3,6,9.

I agree that Sudoku is simple logic. So many people take one look and assume it's math related -- and they give up before trying. I am addicted to Sudoku. My husband bought me a Sudoku calendar. Each puzzle is past difficult and really taxes my brain.

Does anyone have tips on how to solve the extremely challenging one? I'm feeling stupid. ;-)

wlaraby3 months ago
Sudoku is simply a logic puzzle. If it's here, it's not there. May not be the fastest way, but I average 2.5-3.5 minutes on an easy puzzle. Just start with 1, find the first 1 and look across, look down, if there are two 1's in that column or row, and only one spot to put a 1 in the remaining block do so. When no easy option presents itself move on to the 2's, and repeat. Another thing to look for is say the top left block has a 1 in the top left, the top middle block is filled except the middle row across but no 1, and the top right block middle row is empty and the bottom right square is empty.
You know the middle block has to be the middle row somewhere, but not where. That said you can fill in the square for the right hand block because you know the middle row is taken.
Last for the comment, look for rows, columns, or blocks with only 2-3 empty spaces when your stumped. You may see that it needs a 1, and a 5, but one of the spaces in a line already use the 5. So you can put the one in that spot and the 5 in the other.
Maybe I'll actually write up my own how too. Ya think?
MattM83 months ago

If anyone is lost or stuck, you can try my simple sudoku solver!

Should be really fast and easy to use. Let me know if you have any feedback!

Mercy MeS4 months ago

Alright its still a god technique but its not fast enough. I need a fast one

Mercy MeS4 months ago

Alright its still a god technique but its not fast enough. I need a fast one

Mercy MeS4 months ago

Wow! I was struggling trying to find a technique to help me with Sudoku and this was it. It was simple and straight to the point and it does work with the hard ones. The only thing wrong is that you do have to think...............TO PICKUP YOUR PENCIL AND ERASE! That is all I thought about. Try this it works

Nice one! You are implicit using some of the solving techniques mentioned here:

lathishR7 months ago


vincent752010 months ago

without thinking is preposterous as the "solution" you give is precisely what we all do when we solve à sudoku ... Exception we do it in our brain and do not write it down.

sorry "except" not "exception"

Difficult to write english without an french auto correct !!!! ;)

What's the point in solving a sudoku without thinking? There's no pride or "retribution".
R6LPW2 years ago
Using computer programmes to solve Sodoku seems to defeat the object of trying to solve a puzzle or problem to exercise the brain!
Presumably 'broper's somewhat exotic spelling is not for real!
(who is Ible?)
nafango226 years ago
this doesnt work with very hard sudoku puzzles. the really tricky ones will make you randomly pick a number for a square and check to make sure it works in that square as you fill more in.
I have done many "genius level" Sudokus without guessing. There is no need to guess. If you are interested, I'll put up the information on a wordpress blog that works for me.
AnJo888 amannuc2 years ago
Thank you. Please, do that.
Snowbunny8 years ago
I picked up my first puzzle and applied this technique. I failed then copied the puzzle again and took my time. Unfortunately the puzzle was labeled "gold" or "Hard" and I still have a few squares left with a lot needing the same numbers. Is there some sort of "next step" or should I just "hit and miss" and take the "keep trying approach"? Any suggestions?
No need to guess. If you are interested, I can provide additional clues.
AnJo888 amannuc2 years ago
Thank you. Please, do that.
flarr2 years ago
whats the matter with some of you,this is the easyiest systemi have ever seen I just solved the outlaw level3 times with out a hitch,simple just fallw instructions thank you

love this system
what to do when 1 to 9 numbers already exist in column & row of particular block....

man pscovio
deau_oow2 years ago
Sudoku mean a mathematics, brainstorming and calculation. you are completely wrong if "Don't even to think" for sudoku. This is kind of joke of the day for me. by using your above 10 step technique, only simple sudoku's could be solved not even medium, forgot about hard, tough and evils. not even 2% of the puzzle will be solved using these approach.
iyyanar45652 years ago
but i need quick method
There is no quick method. You're supposed to relax and think.
If you guys have an iphone or ipod I thought Pennypop's sudoku app had a really nice learning curve. I picked it up pretty fast and I'm not really that smart :P. it's free too and looks way better than the other apps.
rjvkshl2 years ago
I find SUDOKU to be a very refreshing and mind-invigorating game. If I solve a puzzle with my morning cuppa tea, it helps me to clear my hangover. If I solve a puzzle with my lunch, it helps me to dose off to a peaceful nap.
Prasamsa2 years ago
same quadrant here means??how much area is considered as a quadrant??im confused in this step..
A square of 3x3 is a quadrant or grid. There are 9 of them in the puzzle.
I'm pretty sure he just means one out of the nine "boxes" in the main grid. I guess if "nona-" is the prefix for "nine", then he'd be talking about a "nonadrant". LOL
I came to this web site hoping to find out where my thinking is muddled when I get down to the same three possible numbers in any box, column, and/or row. I can't seem to figure out how to further eliminate possibilities. If you - or anyone else reading this post - can help, I'll check back!
Granny H
You shouldn't end up with a solution where there are only three boxes left, and you have the same three numbers for each of them. In that case, it seems like you could allocate the numbers as you please, as any will be a "right" answer.

If you just have a place where you have the same three numbers appearing in the same box, column, and row, but there are other bits left to solve as well, try to work on other parts of the puzzle. Somewhere in the puzzle, there's some way to eliminate some of those numbers. You might wind up coming at it from a really backward direction, but it's there.
Thank you for trying to help, PurpleKat.

I think I stated my problem poorly. Let's see ... What I meant was more like what you say in your second paragraph. When I have several "other bits" of the puzzle left here and there, and the same two or three numbers are the only ones available for all of those little boxes, I don't know how to eliminate without guessing. And guessing NEVER works for me! I'll come back again when I bump into a good example to give you.

Again, thanks!
Granny H
If I could see a puzzle with the problem on it, I could tell you how I'd go about solving it, assuming I knew how. I'm not a master at this -- just someone who loved logic problems as a kid. :)
rjvkshl2 years ago
You have painstakingly described a beginner's method which I had adopted a few years back. I prefer to 'soften up' the puzzle as much as I can, before embarking on this method, which I have privately termed as the 'slog phase' of solving the puzzle.
How do you soften the puzzle? Select a pattern of rows and columns which have the highest number of digits. Proceed to tackle them in descending order of number of digits.
Once you have selected a row or column with the highest numbers, attack it in an oblique manner. For instance, if you are tackling the upper row, you may find a number repeated in the sub-rows. Now try to fit that number in the 3rd row by looking into the sub-columns.
Attack all 3 horizontal rows and 3 vertical columns turn by turn, systematically in this manner and you would have softened up the puzzle a bit. Repeat the entire process and you'll get a few more discoveries, maybe one or two.
Once the puzzle has become soft, you can start the slog phase. It is NOW that you need a pencil & eraser.
Don't make all entries (from 1-9) in every box. You can straightaway start with the missing numbers ie possibilities.
Once you have entered all possibilities, start looking for singletons - row-wise, column-wise and grid-wise. Having caught singletons, erase the corresponding possibilities row, column and grid wise.
Now look for pairs, triads and even in a few cases, 4-digit patterns. Having identified a pair, triad or a quad in a row/column/grid, proceed to erase the numbers in the remaining possibilities.
Don't forget, once you have discovered any digit, always look obliquely in horizontal as well as vertical directions to fit it into a suitable blank space, as I have described in para 3 above. It helps.
Ultimately you will reach a point where all the solutions cascade into view.
bobc40123 years ago
While this approach is good for solving the simplest of Sudoku puzzles, it is only a start on the more difficult puzzles. Once you have "captured" some of the squares in the more difficult puzzles, you will find a number of squares where it looks like "guess work", when it actually requires "advanced techniques" to solve the puzzle There are techniques like "X-Wing", XY-Wing" an even "multi-color" solutions, to name a few. The site has an ".exe" file that can be downloaded (free) and is useful for solving hard Sudoku puzzles (it has a decent help guide along with googling some of the advanced solving techniques). When you get stumped, you can click on the "hint" button and it will indicate a square and the technique to derive the answer for that square. In certain instances, the technique isn't always straight forward and googling will help clarify.

One thing that is the case with most Sudoku puzzles is the symmetry. You notice the symmetry at the start and as the solution proceeds, you will notice a symmetry in the solution. In this case, this is where I agree with Eddie Chong on the "beauty" of the puzzle. What I detest most are those puzzles where you are reduced to guessing (rather than using logic and reasoning) which of 2 or 3 numbers to to choose in 2 or 3 squares and use "trial and error" to solve. This is typical in most Sudoku magazines that have "extreme" or "brutal" puzzles. To me, you should never have to resort to "trial and error" to solve the puzzle. As Sir Arthur Conan Doyle had Sherlock holmes say "Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth."
10T3 years ago
It's great to see all the comments from so many dedicated puzzle solvers! I just started Sudoku, so using this technique along with tips from other websites really helped me to learn the methods quickly, for example, solving by pairs and triples. Thanks for creating this website.
broper3 years ago
very nice
good job on you ible but one thing i want to menchon dosint this methoud take the fun out of sudoku? i tryed it on a hard puzzel and i didn't feel like i completed any thing when i was fineshed.

nice way to do it but it takes the fun away
I disagree... if you used this method on truly hard puzzles, even with "notes" (as I call them) they can be difficult. A puzzle is a problem meant to be solved, this happens to streamline the process. Goodluck :)
yes thats a good point but i think it makes it to easy i mean i like doing hard puzzles and i enjoy the chalenge but if i do it the way you suggest i think it makes it two easy


i think the methoud you made is a good one and i have nothing roung with it
it does its job it makes sudoku easy ( :
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