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# Sudoku

Sudoku is a puzzle utilizing a nine by nine square grid. The boxes are grouped as shown in the diagram. The object is to fill out the numbers, one through nine, so that each digit appears only once in each row, each column or in each nine square grouping. For each puzzle there is only one solution. They range in difficulty from easy to very hard depending on which (and how many) squares are filled in. The number of possible puzzles is incredibly high; the number of 81 square combinations is 6,670,903,752,021,072,936,960.

Sudoku was invented by Howard Garns of Indianapolis, but he called it "number place". The first puzzle appeared in "Dell Pencil Puzzles and Word Games" in 1979. The puzzle did not immediately catch on in the United States, but would return, with a vengeance, via a vicarious route. A Japanese puzzle expert, Nobuhiko Kanamoto, saw the puzzle in the U.S. and took it back to Japan with him. He made a few minor adjustments and renamed it Sudoku. "Sudoku" means "single number" in Japanese.

A New Zealand lawyer, Wayne Gould, picked up a Japanese Sudoku magazine and became so enamored with the puzzle that he spent six years writing a program that could automatically generate the puzzles. He sold the idea of publishing the puzzles to the Times newspaper of London. The paper began to print the puzzles in November of 2004. Once London went crazy over Sudoku it hit U.S. newspapers and spread swiftly to the internet.

Strategies for solving Sudoku puzzles vary. However, the method advocated by "SudokuToday.com" involves three major steps, scanning, marking and analyzing. Scanning is done at the beginning by crosshatching, going through all the rows columns and boxes and determining any easy fill-ins by the process of elimination. Easy puzzles can often be solved by using scanning alone.

Marking is the next step. This is done by using subscript to write the possible numbers in each square. Alternatively, puzzlers may use the dot method, placing a dot at intervals in the square (upper-left being one and lower-right being nine).

Analysis of the most promising region, column or row then should be undertaken, finding by the process of elimination the logical number to appear in a particular square. When one number is found, it will affect possibilities in other squares within the row, column or region in which it resides. Return to step two and mark all of the affected squares (crossing out the numbers that no longer may fill the square or adjusting the dots). Repeat this process until the puzzle is completely solved.

W.J. Rayment

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