sudoku or su doku [Jap.,=single number], a number puzzle consisting, in its classic form, of a square divided into nine squares, with each smaller square divided into nine boxes, thus forming an overall grid of 81 boxes. To solve the puzzle, a single number (from 1 to 9) must be entered in each blank box so that each number is used only once in each smaller square and only once in each row and column in the larger square. A number of the boxes are always filled in by the maker of the puzzle, providing both clues and limitations to where the solver may place numbers, and the degree of difficulty of the puzzle is determined by which numbers the puzzle maker chooses to reveal as clues. Variations include the use of larger or smaller squares than the 9-box-by-9-box classic grid, irregular divisions of the overall grid, and additional restrictions on the placement of the numbers.

The modern origins of sudoku appear to lie with Dell Puzzle Magazines, which has published nine-square "Number Place" puzzles since the 1970s. Such puzzles are based on, but more complicated than, the Latin squares described by the 18th-century Swiss mathematician Euler. In 1984 Nikoli publishers began publishing sudoku puzzles in Japan. Nikoli limited the number of boxes filled in as clues to less than 30, and required that the clues form a symmetrical pattern. In this form sudoku became popular in Japan and by 2005 common in the United States and other countries.

also known as Su Doku

Encyclopædia Britannica, Inc.Puzzle in which numbers are filled into a grid subject to certain constraints. In its simplest form, sudoku consists of a 9 × 9 grid with numbers appearing in some of the squares. The object of the puzzle is to fill the remaining squares, using all the numbers 1–9 exactly once in each row, column, and the nine 3 × 3 subgrids. Sudoku is based entirely on logic, and the level of difficulty is determined by the quantity and positions of the original numbers.

The first known appearance of sudoku was in 1979 in a New York-based puzzle magazine, which called them Number Place puzzles. They next appeared in 1984 in a magazine in Japan, where they acquired the name sudoku (abbreviated from suuji wa dokushin ni kagiru, meaning “the numbers must remain single”). In spite of the puzzle's popularity in Japan, the worldwide sudoku explosion had to wait another 20 years.

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