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Sudoku: Rules and Strategies

Raza Khan

© Raza Khan 2006

An introduction to the rules and strategies of the popular puzzle game - Sudoku. A game that originated in Japan, but is now spread all over the world. The strategies that are discussed include: Elimination Strategy; ICU Strategy; and the Supposition Technique.
Enter Sudoku - a game that has taken the world by storm. It’s the new craze in town. It originated in Japan, but is now spread all over the world. It has spread like wildfire and everyone has got into it. But now, what is Sudoku? Sudoku is a game where numbers are to be represented on a grid in a special pattern (see below). And no! It’s not about math, it is purely logic. A logical sequence is what one has to make. You have to know nothing about math. Alternatively, letters of the alphabet or different symbols can also be used. The Sudoku puzzle is an innovative creation, and the best part is that it’s great fun! It is just a puzzle which has so many variations and there are so many possibilities the one can never get bored. Every time, Sudoku offers a different challenge. The main advantage of Sudoku is that it is really inexpensive and it is free on the web. So, if you have a computer, you’re off!

Playing Sudoku

Now, let’s get to it! How to play! Well, the rules are fairly simple, straightforward and easy to understand. The only aim of the puzzle is to enter an integer from 1 to 9 (or if you are using alphabets, A to I) in each cell of a 9x9 grid. The big 9x9 grid is itself made up of nine, small 3x3 sub-grids which are known as regions. Each puzzle already contains a few numerals filled in and by using this information, one has to achieve his goal. But, the hard part is that each row, column and region must contain only one instance of each number. For example, a row which has “1” in it cannot contain any other “1” so you know that the other squares in that row do not contain a “1”. Well, that’s how it works and you have seen for yourself: no math, just logic.

After rules come strategies, and there are quite of them. I should first tell that the puzzle comes in very easy to extremely hard levels so you can easily choose your beginning level and progress from that place. Following are a few strategies and I’m sure that you will be able to develop some more of your own:

Elimination Strategy

The first and most basic strategy is the elimination strategy. Choose a number that appears a few times in the puzzle. Now in those rows and columns in which the number occurs, that number won’t be there. You have actually eliminated those squares from your choice, which is now very little. Now, some regions are such that only one square remains in which the chosen numeral can occur. So, you have filled that square. Nice and easy does the trick!

ICU Strategy

Another strategy is the ICU or the I-Choose-U strategy. It is that you choose a good region i.e. many of it’s squares are filled. Then choose an empty square in it. First of all, that square does not contain any number from that region. Secondly, that square does not contain any numbers of that row or of that column. Usually, only one possible number is left and you’ve filled another square.

Supposition Technique

This is a rather complicated strategy but an equally good one. The aim of the strategy is to deduce the row or column of a number but not it’s exact position. By using this information, one can find the position of the same number in a different region. For example, one column of a region is filled up with number other than, for example, “7”. If there is a “7” in another column below or above that region in another region, then you know that “7” is not in that column as well. So now only one column of the previous region is left in which “7” can occur. Now that you know “7” is in that column, you can use this information to your advantage by eliminating more squares.


Well, that’s it for Sudoku. C’mon. Play Sudoku. I’m sure it will be proud to heave another entry in it’s enormous fan list.

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