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.
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.
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.
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.
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.
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.
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.
Step 6: Repeat for all the pre-printed numbers
Just repeat thos three steps for each number that was printed in the puzzle. The purpose of the down, across, and circle marks on each number is to provide for any interruption that may occur when solving the puzzle. By drawling those lines you can always tell exactly where you left off. If the number has all three marks, you can be sure that all of the corresponding numbers have been eliminated from the puzzle. YOu can effectively forget about that block now.
Let's see what the result of all that erasing was.
Let's see what the result of all that erasing was.
Step 7: Locate Answers
By process of elimination you will have done so much erasing in some blocks that only one number is left. Guess what. THat is the answer for that block. Congratulate yourself.
Write that number large in the block, then treat it like a preprinted number. Eliminate all the across, down and around numbers as you have already done so many times before.
In this image, the red pen points point to all the answers that were provided just by doing the initial erasing.
We have not yet begun to think!
Write that number large in the block, then treat it like a preprinted number. Eliminate all the across, down and around numbers as you have already done so many times before.
In this image, the red pen points point to all the answers that were provided just by doing the initial erasing.
We have not yet begun to think!
Step 8: Other kinds of eliminations.
You won't always be so lucky. Not every time will you end up erasing all the numbers but one in a block. If that is the case, then you peruse the puzzle to find eliminations.
First look down each column. If you find a number that only appears in one block in a column. That is the answer for that block.
In this picture, the pen point points to a three. That is the only three in that column, so that must be where it goes.
Write it large, then treat it like a pre-printed number. See ... this isn't thinking. This is EASY.
First look down each column. If you find a number that only appears in one block in a column. That is the answer for that block.
In this picture, the pen point points to a three. That is the only three in that column, so that must be where it goes.
Write it large, then treat it like a pre-printed number. See ... this isn't thinking. This is EASY.
Step 9: Look Around a quadrant.
I know, they aren't really quadrants, but you know what I mean, don't you?
If you've looked across the columns, and across the rows and there are all duplicates, then look in the group. If there is one number in the group that only appears in one block, then it's your answer.
See... There is no guessing in Sudoku. One of these situations has to occur. You just need to find them.
IN this picture the 5 only appears in one block in the group. It goes there.
Write it big, then treat it like a pre-printed number.
See where we're going, here?
If you've looked across the columns, and across the rows and there are all duplicates, then look in the group. If there is one number in the group that only appears in one block, then it's your answer.
See... There is no guessing in Sudoku. One of these situations has to occur. You just need to find them.
IN this picture the 5 only appears in one block in the group. It goes there.
Write it big, then treat it like a pre-printed number.
See where we're going, here?
Step 10: Lather, rinse repeat.
Eventually, you will find all those lonely numbers in thier rows, columns or groups.
Remember to draw those lines and circles in case you get interrupted.
Eventually you will solve the puzzle.
Compare our solution to the "Official Solution" found on the Sudoku.com site. See? A perfect match.
And you thought Sudoku was hard.
It's so easy, you don't even have to think!
Remember to draw those lines and circles in case you get interrupted.
Eventually you will solve the puzzle.
Compare our solution to the "Official Solution" found on the Sudoku.com site. See? A perfect match.
And you thought Sudoku was hard.
It's so easy, you don't even have to think!
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Presumably 'broper's somewhat exotic spelling is not for real!
(who is Ible?)
love this system
man pscovio
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
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.
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
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.
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."
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
my dad is always sayin' that it has to be chalenging
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 ( :
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.
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 !!!…
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.
This is nott a game of memory, it is a game of systematically solving a grid puzzle.