6 Ways to Solve a Sudoku - wikiHow.pdf

4/24/2015 6 Ways to Solve a Sudoku - wikiHow

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How to Solve a SudokuSix Methods: Easy Difficulty Hard Difficulty Samurai Sudoku Killer Samurai Sudoku

Sample Sudoku Puzzles Blank Sudoku Template

Sudoku is a numbers puzzle that has swept the world. It is very fun to play, but

can be tricky and confusing at first. The objective of the puzzle is to put the

numbers 1-9 in every row, column, and 3x3 square block.

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Use the counting principles to solve the puzzles. Since you already know that

you can't have the same number in any row, column, or nine-square block, you can

use that to help you get a number. The difficulty depends on the placement of the numbers

given to you.

Seek "definites". When solving an easy Sudoku, the first thing you should do is look

for definites. Definites are numbers that are definitely going to be there. Starting at 1,

draw imaginary lines through boxes in that 1's row and/or column. When there is only one

box left in the 3x3 box, you know that is a definite. (See images one and two).

Work your way through the numbers until 9. Since you have filled in some

numbers, this should help get other numbers that had more than one possibility

before. (See images three and four. Notice how the 3s could not have been solved before,

but are solved in the final).

Look again when stuck. If you get stuck, go back and make sure to look at

everything. It is almost guaranteed you missed something. That one number is usually

all you need to get going again. If you still cannot find any solutions, start labeling every

block with every number that could possibly go in that box.

For example, in image one, all the empty boxes have numbers that could possibly

go there. Fill these in. If there is a 1 in the row or column of that box, you know that

1 is not a possibility.

Sudoku Puzzle

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Method 1 of 4: Easy Difficulty



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Start by doing Sudoku in the newspaper or online (see links below). The

newspaper sudokus are usually easier on Monday and Tuesday. The difficulty

increases as the week passes.

Try your hand at harder Sudokus. This particular Sudoku (images one through

four above) could be solved with only definites, but what do you do if it can't?

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Start at number 1. Use the same logic from an easy puzzle to fill in every empty box

with all of the possible numbers for that box. If possible, put in definites. For example,

picture three (above) shows that you can't solve for 3.

In a hard Sudoku, you won't be able to solve from the start, so just fill in what you

know it could be. This will help later when you have two or three options per box

and you can't remember what they are.

Note that if two boxes in a block, column or row must be one of two numbers,

you can use those numbers to eliminate other possibilities. For example, in a

block, there are four open boxes. From your analysis, you have determined that:

box A can be 1, 2, 3, or 4;

box B can be 1, 2, 3, or 4;

box C can be 3 or 4; and

box D can be 3 or 4.

From this we know that box A and B cannot be 3 or 4, because they have

to be either 1 or 2. Box C and D have to be either 3 or 4. This information

might be useful in solving other boxes.

Recognize that hard Sudokus can take time - a lot of time. A hard Sudoku can

actually take days to complete, but they are still fun. The harder they are, the more fun

it is when you finish. A hard Sudoku can be solved the same as an easy one, it just gives

you less to start with. The logic of a hard puzzle is that if you know everything that can go in

every box, it is very simple.

For example, say you have two possible 2's for a particular nine-square box, and

they are in a row or column and you know that 2's cannot go anywhere else in the

nine-square box. This means that you know that the row or column those 2's are in

Method 2 of 4: Hard Difficulty



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cannot have 2's in it except in this nine-square box. This sounds confusing, but

when applied, it is actually very easy and it helps a lot.

Consider this alternative, surefire way to always solve a puzzle accurately

and quickly. In this method, fill in each block with all the possible numbers that could

go there. Write all the numbers small at the top of the block. You can recreate the puzzle on

bigger paper to help with this. Write all the numbers that don't appear in that row, column or

square. Once you have done this for a whole column or row, start filling in the obvious

answers. You will have solved the puzzle by the time you do this for every row.

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Be a confident and advanced Sudoku player. The Samurai Sudoku puzzle is a

puzzle only to be attempted by a skilled Sudoku solver. It is basically five Sudokus in

one. The corners of each are interconnected with a middle puzzle (see image below).

These puzzles can be long and difficult.

Keep the connections in sight. When solving these, you must always remember

that the corner connected with the center puzzle must work with both puzzles.

Look at the lines. The lines that are twenty-one boxes long are going to be looked at

as if there were three separate nine block lines, one of which is comprised of pieces

of the other two.

Solve just as you would a regular puzzle. Just remember that you can have up to

three of the same number in lines that connect to the center puzzle.

See External Links below for Samurai Puzzles.

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Method 3 of 4: Samurai Sudoku



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Take a look at the killer variant of the samurai Sudoku. The rules are a bit

different, and the grid now involves color. The standard Sudoku rules apply to this

puzzle as well, i.e. each nine square box has to have the numbers 1-9

Killer Samurai Rules

Look within each of the colored blocks for a small number. This denotes the

total value of the squares within that block. For example, if a colored block comprising

3 squares totals 7, then the individual squares must be 1, 2 and 4, but it is down to the

reader to ascertain in which order they must be placed.

Notice that within each colored block, a number may be repeated, although

this is rare.

Note the total. Each nine square block must total 45, as must every row and column.

Realize that in a Killer Samurai puzzle there are 4 instances where 3 x 3 grids

belong to two different nine square blocks. In this situation the same rules of

Sudoku apply, i.e. the numbers 1 9 must be used once only. It stands to reason that these

4 grids can hold the key to solving the entire puzzle.

Advice for Solving the Puzzle

Look for colored blocks which contain high or low totals. These have fewer

combinations of numbers and are, as such, easier to solve.

Look for a group of colored blocks which protrude beyond the boundary of

the nine square blocks by one square only. This will allow the reader to

determine at least one square of a colored block.

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Method 4 of 4: Killer Samurai Sudoku



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Don't just think of a single block totaling 45. It may sometimes be possible to

ascertain a number by adding colored blocks in 2, 3, 4 or more nine square blocks

totaling 90, 135, 180 etc to ascertain a single elusive number.

Look for intersecting colored blocks with high or low totals. For example,

where a colored block totaling 3 is at 90 degrees to a colored block totaling 4, the

values of the blocks should be easy to work out as there is only a choice of 3 numbers; 1, 2

and 3, but don`t forget that each row and column must contain the numbers 1 9 once only.

Look to eliminate 'pairs'. If a colored block of 2 squares totals 4, 6, 8 etc., logic tells

you that the numbers contained within cannot be 2 & 2, 3 & 3 and 4 & 4 etc. thus

reducing the permutations.

Look for colored blocks that form 'lines'. For example, if 4 colored blocks of 2

squares form a line, then the missing number can be calculated by deducting the total

from 45.

Number Combinations

Be aware of 2 square combinations. These include:

Be aware of 3 square combinations. These include:

Try less advanced Sudoku before moving on to Killer Samurai Sudoku. Killer

Samurai Sudoku is an advanced variant of Sudoku and it is highly recommended that

you try to complete a normal and also Samurai Sudoku before undertaking these more

complex puzzles. These are extremely hard puzzles. They may take days to complete. Just

have patience.

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Sample Easy Sudoku Sample Intermediate

Sudoku

Sample Hard Sudoku

Blank Sudoku Template

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Your speed increases with regular practice.

Another good place to practice your Sudoku skills is in a book. There are

many books with Sudoku puzzles in them. Some even have step by step

instructions to improve even more.

Have contests with your friends or coworkers. Make copies of a puzzle

Sample Sudoku Puzzles

Blank Sudoku Template

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Tips

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and try to see who can finish the fastest. Doing this once a day or once a

week will help to dramatically increase your speed.

Instead of writing numbers, imagine each square as a 3x3 grid of dots. A

dot in the upper right corner is a 3, one in the middle is a 5. This method

involves less clutter in each box.

Go by box, then by row, then column.

Try to find the obvious first.

Check twice, put a number once.

Copy the puzzle onto a grid much bigger than the ones in the

newspaper, using a marker. Now solve the puzzle using the bigger

squares to clearly write in pencil all the possible numbers.

If you're having a block, stop, and take a break for a couple hours. Take

a nap, do some errands, play a game, etc.

Use the web-pages below to help you. They are all very useful, but try to

stay away from the auto-fillers. Where is the fun if the computer does it

all for you?

Before using solvers, try to solve it yourself. Where is the fun if

something else solves it for you?

Try to look at the puzzle both ways; rather than working north to south all

the time, try east to west. Remember, it's always a good idea to look

both ways before crossing the street.

For every cell you fill in, make sure you double, or even triple check your

logic; one single error could mess up the entire puzzle. If you are almost

sure a three can go in a box, triple check why you think this. If there is

even a remote possibility of a three going in a different box, don't put a

number down! Many a person has almost finished a puzzle only to find

that they put one number in the wrong place.

It is considered cheating if you guess at where a number could be. All

true Sudoku puzzles are solvable with only logic. If there are two

possible numbers that could go in a space and you just choose one and

hope it's right, this is cheating.

Warnings



Time

10-20 minutes for easy to medium after you've become a little

experienced.

30-45 minutes for medium to hard.

1-4 hours for Samurai (unless you are very skilled).

4 hours+ for Killer Samurai

Pencils

Erasers

Patience

Logical ability

Sudopedia

Sudoku Essentials

Wikipedia on Sudoku

Thanks to all authors for creating a page that has been read 1,422,988 times.

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In other languages:

Italiano: Risolvere il Sudoku, Espaol: resolver un sudoku, Portugus: Resolver um

Sudoku, Nederlands: Een sudoku oplossen, Franais: russir un

sudoku, Deutsch: Sudokus lsen, : , Bahasa

Indonesia: Memecahkan Teka teki Sudoku, etina: Jak vylutit Sudoku, :

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6 Ways to Solve a Sudoku - wikiHow.pdf