Sudoku is a logic-based, combinatorial number-placement puzzle type. Formerly known as the “Number Place”, the objective of the puzzle is for the player to fill a 9x9 grid with digits so that every column, row, and nine 3x3 sub-grids comprising the entire grid will have all of the digits from 1 through 9. The grid here is also called as sub-squares, blocks, regions, or boxes.

History of Sudoku:

On the 6th of July, 1895, Le Siècle's rival, La France, refined the late 19th century number puzzle so that it almost resembled the modern Sudoku. It simplified the 9×9 magic square puzzle so that every row, column and broken diagonals consisted of only the numbers 1 through 9, but did not mark the sub-squares. Even though they are not marked, every 3×3 sub-square comprises the numbers 1 through 9, with the added constraint on the broken diagonals leading to only a single solution.

The modern Sudoku was theoretically designed by Howard Garns, who was a retired architect and freelance puzzle constructor hailing from Connersville, Indiana, and first published in 1979 by Dell Magazines as the “Number Place”. Garns is said to be the anonymous designer of the puzzle as his name constantly appeared on the list of contributors in the issues of Dell Pencil Puzzles and Word Games that included the Number Place, and was always absent from issues that did not. Unfortunately, Garns died in the year 1989, and that was before getting a chance to see his own creation as a worldwide sensation.

Variations of Sudoku:

Even though the 9×9 grid with 3×3 regions is considered to be the most common format, there are actually a lot of other variations of the puzzle. There are puzzles consisting of 4×4 grids with 2×2 regions, 5×5 grids with pentomino regions, and 6×6 grids with 2×3 regions (World Puzzle Championship). Additionally, there is also a puzzle with 7×7 grids with 6 heptomino regions with a disjoint region.

Sudoku with bigger grids also exist. The Times offers a 12×12-grid with 12 regions of 4×3 squares (Dodeka Sudoku). Dell Magazines regularly publishes 16×16 puzzles called the Number Place Challenger, having 16×16 variant that uses 1 through G instead of the 0 through F used in hexadecimal. A 100×100-grid puzzle called the “Sudoku-zilla” was published in the year 2010.