Sudoku Puzzle Network
About Sudoku
Sudoku, sometimes spelled Su Doku, is a placement puzzle, also known as Number Place in the United States. The aim of the puzzle is to enter a numeral from 1 through 9 in each cell of a grid, most frequently a 9×9 grid made up of 3×3 subgrids (called "regions"), starting with various numerals given in some cells (the "givens"). Each row, column and region must contain only one instance of each numeral. Completing the puzzle requires patience and logical ability. Its grid layout is reminiscent of other newspaper puzzles like crosswords and chess problems. Sudoku initially became popular in Japan in 1986 and attained international popularity in 2005.
Introduction
The word Sudoku means "single number in an alloted place" in Japanese. The numerals in Sudoku puzzles are used for convenience; arithmetic relationships between numerals are absolutely irrelevant. Any set of distinct symbols will do; letters, shapes, or colours may be used without altering the rules (Penny Press' Scramblets and Knight Features Syndicate's Sudoku Word both use letters). Dell Magazines, the puzzle's originator, has been using numerals for Number Place in its magazines since they first published it over 25 years ago. Numerals are used throughout this article.
The attraction of the puzzle is that the completion rules are simple, yet the line of reasoning required to reach the completion may be difficult. Published puzzles often are ranked in terms of difficulty. The difficulty of the puzzle depends upon how easy it is to logically determine subsequent numbers. Perhaps surprisingly, the number of givens has little or no bearing on a puzzle's difficulty. Puzzles with a minimum number of givens can be very easy to solve, and puzzles with more than the average number of givens can still be extremely difficult to solve.
Sudoku is recommended by some teachers as an exercise in logical reasoning. The level of difficulty of the puzzles can be selected to suit the audience. The puzzles are often available free from published sources and also may be custom-generated using software.
Rules and terminology
The puzzle is most frequently a 9×9 grid made up of 3×3 subgrids (called "regions"). Some cells already contain numbers, known as "givens". The goal is to fill in the empty cells, one number in each, so that each column, row, and region contains the numbers 1–9 exactly once. Each number in the solution therefore occurs only once in each of three "directions", hence the "single numbers" implied by the puzzle's name.
(Reprinted From Wikipedia, the free encyclopedia)
Licensed under the GNU Free Documentation License this article uses material from the Wikipedia article "Sudoku"