Solve Sudoku (Without even thinking!)

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.

Step 1: What you need to begin

You need:

1. A sudoku puzzle. I enlarged this one (which was the puzzle that appeared on Sudoku.com 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.

Comments

[chocolateface]

What's the point in solving a sudoku without thinking? There's no pride or "retribution".

[R6LPW]

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?)

[nafango22]

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.

[amannuc]

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]

Thank you. Please, do that.

[Snowbunny]

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?

[amannuc]

No need to guess. If you are interested, I can provide additional clues.

[AnJo888]

Thank you. Please, do that.

[flarr]

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

[sankalpsawant]

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

[sankalpsawant]

man pscovio

[deau_oow]

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.

[iyyanar4565]

but i need quick method

[kokosalexa]

There is no quick method. You're supposed to relax and think.

[iloveswing95]

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.

[rjvkshl]

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.

[Prasamsa]

same quadrant here means??how much area is considered as a quadrant??im confused in this step..

[rjvkshl]

A square of 3x3 is a quadrant or grid. There are 9 of them in the puzzle.

[Granny Hardin]

Prasamsa,
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!
Thanks!
Granny H

[PurpleKat]

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.

[Granny Hardin]

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

[PurpleKat]

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. :)

[rjvkshl]

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.

[bobc4012]

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 http://www.angusj.com/sudoku/ 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."

[10T]

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.

[broper]

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

[hrodriguez7]

you have a point


my dad is always sayin' that it has to be chalenging

[broper]

tx ( : i think the way you do it is awsom. and smart that you came up with it

[parallelchild]

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 :)

[broper]

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


ps

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 ( :

[mitchell12]

Try cross words, Seems like you'd have plenty of challenge with those :)

[WillyTheKid]

I try to get everybody I know to play Killer Sudoku (or Sum-doku). So much more of a challenge than even the hard level sudokus. but still there is a system.. always a system, even if it is complex. no need to guess!

[bjohnson1]

You should only use a pen and no eraser! That is how to do Sudoku.

[siamonsez]

I'm sorry, but this method feels like cheating to me, and at the very least defeats the purpose of doing the puzzle in the first place. You can resort to this method once the majority of the puzzle is done and you are totally stuck, but in my experience, you only get stuck because you either missed something obvious, made a mistake, of are trying a puzzle above your skill level that requires the use of techniques you are not familiar with.
Anyone that wants to learn to sudoku should avoid this technique because you will learn nothing by finishing puzzles this way and therefor will never be able to progress on to more challenging puzzles.

[vincent7520]

right !…
100% !…
I'm not against cheating, but it's got be worth it. In this example we didn't even try to begin to play sudoku : may as well play pencil and eraser on any piece of paper.
anyway… the example given is so basic that it's not even worth taking the pain to write all those numbers down : this sudoku can nearly be solved by itself !!!…

[bwrussell]

This is simply a visual representation of what your thought processes when finding the answers. The only reason it's easier is that you don't have to remember everything you've done. Of course more advanced puzzles will require more advanced techniques but a lot of those techniques are based on logical trial and error, which could be considered cheating just as much as this method.

This is a good way to start if you are learning sudoku, eventually you will learn the patterns and you wont need as many pencil marks. Besides if you are just starting and need this method to solve a puzzle there is little chance that you will know or be able to use the more advanced techniques.

[Eirinn]

I really cannot see what the difference is? The only difference i see is that this is systematic and the other way of doing it is less systematic.

This is nott a game of memory, it is a game of systematically solving a grid puzzle.

[siamonsez]

The difference is that if you rely on this method you will never get better. Once you start doing sudoku puzzles regularly, it's not just about completing them, but doing it quickly; anyone can finish , what makes it fun is doing it better.

[Eirinn]

The answer to this problem is not as straightforward as that :) It all depends in which way one views "getting better" and "fun".

[siamonsez]

Maybe I have a bit of ADD, but once something gets monotonous, it gets boring. So, for me, pushing myself to do better is what makes it fun; therefore, the two are interchangeable.