Sudoku

A typical Sūdoku puzzle

Sūdoku (数独 "single numbers") is a mathematical, logic-based puzzle, where the aim is to complete a 9x9 grid, so that each row, column and 3x3 grid contains only one recurrence of the digits from one to nine.

The game has its roots in the games of "Latin Squares", invented by the Swiss mathematician, Leonhard Euler, in the 1780s. He developed the idea of arranging numbers in such a way that any number or symbol would occur only once in each row or column.

Sūdoku as we know it today, was invented by the retired architect, Howard Garns, and first appeared, as "Number Place" in Dell Magazines in 1979. The puzzle was later introduced to Japan in 1984 and was originally called Suuji wa dokushin ni kagiru (数字は独身に限る), meaning "no more than one of each digit". This was later shortened to "sūdoku". At the same time, the maximum number of "givens", or revealed cells, was limited to 32. The fewer "givens", the harder the puzzle. As with crosswords, the puzzles were also symmetrical.

It was not until Wayne Gould, a retired Hong Kong judge, discovered the game and enjoyed it so much that he began creating his own puzzles that the game really caught on internationally. He began submitting his puzzles to The Times of London, which began publishing them in 2004, under the name Su Doku. From there, it crossed the ocean back to America. Today, most major newspapers carry a Sūdoku puzzle.

Typically, the grid is 9x9. Variations of the puzzle include 4x4 (with 4 smaller 2x2 grids), 16x16 (with 16 smaller 4x4 grids), and 6x6 (with 6 smaller 2x3 grids).