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Introduction

A Brief History

The puzzle we now know as Sudoku began life under a different name. In 1979, Howard Garns designed a number-placement puzzle for Dell Magazines and called it “Number Place.” It quietly circulated in puzzle books for several years before reaching Japan in 1984, where the publisher Nikoli rebranded it “Sudoku” — a contraction of a Japanese phrase meaning roughly that the digits in the grid must each appear only once. The shorter name caught on globally, although in Japan itself Nikoli holds the trademark, and other Japanese publishers refer to the same puzzle as “Nanpure” (a phonetic rendering of “Number Place”).

The Western boom came in late 2004, when Wayne Gould — the founder of Pappocom — convinced The Times of London to print a daily Sudoku. From there it spread across European newspapers and on to the rest of the world. Within months, Sudoku books, magazines, and websites were everywhere, and the puzzle had attracted a sizeable population of enthusiasts who play it daily.

The Grid

The standard Sudoku puzzle is played on a 9×9 grid containing 81 cells. Variations of the puzzle use grids of other sizes, but the 9×9 form is the one most people mean when they say “Sudoku.” Each cell is either empty or filled with a single digit from 1 through 9. A blank cell is simply that — blank. Zeros are not part of the puzzle, although in some printed and electronic versions a zero is used as a placeholder for an empty cell.

Although the puzzle uses numerals, it is not a math puzzle. No arithmetic is required to solve it. The digits are simply nine distinguishable symbols, and you could replace them with letters, colors, shapes, or any other set of nine markers without changing the puzzle in any way. Digits are used because they are the most compact and universally readable symbols available.

The Rule

There is one rule, and it has three parts. The completed grid must contain each of the digits 1 through 9 exactly once in every row, exactly once in every column, and exactly once in every 3×3 box. The 3×3 boxes are the nine non-overlapping square regions marked by the heavy lines on a printed Sudoku grid.

The Givens

A Sudoku puzzle is set with some of the cells already filled in by the puzzle’s composer. These pre-filled digits are known as givens, clues, or fixed digits. They cannot be changed; the solver’s task is to fill in the remaining cells. A well-formed puzzle has exactly one solution, and that solution can be reached by logical deduction alone — no guessing required, however complex the deduction may need to be.

How to Proceed

Now that you have a sense of what Sudoku is, the next steps are:

• Get familiar with the Diagrams and Notations used by the Sudoku community to discuss puzzles and techniques.
• Browse the Terminology index to learn the vocabulary that solvers use.
• Read about the Solving Techniques — these are the logical patterns that let you place digits with certainty.