For millennia people has been drawn to things that vexed their minds. Riddles, word and number puzzles – if they involved intense thought they have been adored. The 1970’s saw the widespread love (perhaps for some love-hate) relationship with a simple block containing rotate-able smaller square blocks of different colours called the "Rubik Cube". This year the head scratching, hair pulling and downright addictive game of choice is a Japanese creation by the name of Sudoku.

Like the vast majority of great puzzles Sudoku appears seemingly benign, a simple grid of nine squares, each square containing nine smaller squares (equalling eighty one small squares in total). The nine large ("mother") squares are typically considered to belong to one of the three grids of the puzzle known as regions. Each of the eighty one small squares contains, or will contain upon completion, a numeral between the numbers one and nine.

Even the rules of this game - which sprang to mainstream life in Japan in 1986 – seem relatively straightforward. In order to "win" at Sudoku you must fill in each region, column and row of the grid, no blank spaces can remain. Yet the difficulty begins to factor in when you take into account the rule that says that each of these areas can only contain the number (one through nine) once. Some of the squares already contain numbers, these are referred to as "givens", it’s the player’s job to fill in the empty spaces, whilst adhering to the rule of "one occurrence" for each number in each of the three directions of the puzzle.

Interestingly numbers are really only used for the sake of convenience, as they have no mathematical bearing on the game itself*. They needn’t add up to any sum, or occur in any particular set of patterns. In place of numbers the puzzle can contain shapes, colours, symbols, whatever, as long as the same rule (that each one only appear once in each area of the puzzle) can be applied. Perhaps the allure of the Sudoku lies in the fact that it appears so easy, what’s hard about filling in a few squares, right? Yet one try at this game, and all but the most seasoned logistical puzzle pros will find themselves in a little over their heads. Which isn’t to say that the game can’t be completed, on the contrary it can, and after a while Sudoku "pros" are able to complete a puzzle in a matter of minutes. But this takes work, a lot of work, study and devotion to this unique Japanese square.

The world has certainly jumped on the Sudoku bandwagon, its popularity generating websites (which often feature many free puzzles of varying degrees of difficulty), and regular Sudoku puzzles in many magazines and newspapers, even Sudoku software! With an appearance similar to a crossword puzzle and strategic manoeuvring reminiscent of chess it’s no wonder that Sudoku has sprung forth from Japan and taken on as an international obsession.

*In actuality Sudoku does have a mathematical principle behind it known as the "complexity theory", which classifies Sudoku as a "NP-complete (Non-deterministic Polynomial time) puzzle (or problem)". The "NP" means that a puzzle/problem with this classification is the most difficult problem of its kind to solve. It is a very complex form of math that does not as of yet have a definitive arithmetical solution for each and every Sudoku grid.

Jessica Cander is a professional freelance writer with a passion for puzzle games. A great place to find online info on a wide variety of subjects – including Sudoku – is http://www.answers.com .

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