Sudoku, also known as Su Doku, popular form of number game. In its simplest and most common configuration, 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, without any arithmetic involved, and the level of difficulty is determined by the quantity and positions of the original numbers. The puzzle, however, raised interesting combinatorial problems for mathematicians, two of whom proved in 2005 that there are 6,670,903,752,021,072,936,960 possible sudoku grids.
Although sudoku-type patterns had been used earlier in agricultural design, their first appearance in puzzle form 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.

Basic Rules of Sudoku

• Sudoku grid consists of 9x9 spaces.
• You can use only numbers from 1 to 9.
• Each 3×3 block can only contain numbers from 1 to 9.
• Each vertical column can only contain numbers from 1 to 9.
• Each horizontal row can only contain numbers from 1 to 9.
• Each number in the 3×3 block, vertical column or horizontal row can be used only once.
• The game is over when the whole Sudoku grid is correctly filled with numbers.