# Sudoku

Sudoku (Japanese: 数独, sūdoku), sometimes spelled Su Doku, is a placement puzzle, also known as Number Place in the United States. The aim of the puzzle is to enter a number from 1 through 9 in each cell of a grid, most frequently a 9×9 grid made up of 3×3 subgrids (called “regions”), starting with various numbers given in some cells (the “givens”). Each row, column and region must contain only one instance of each number. Completing the puzzle requires patience and modest logical ability (although some puzzles can be very difficult). Its classic grid layout is reminiscent of other newspaper puzzles like crosswords and chess problems. First published in the United States, Sudoku initially became popular in Japan in 1986 and attained international popularity in 2005.

The numerals in Sudoku puzzles are used for convenience; arithmetic relationships between numerals are not important. Any set of distinct symbols will do; letters, shapes, or colors may be used without altering the rules.

A difficult Sudoku puzzle.

The solution to this puzzle from row one to row nine is:

++++++++++++
|3 9 2|1 8 5|7 4 6|
|8 5 7|4 9 6|1 3 2|
|1 4 6|7 3 2|9 5 8|
++++++++++++
|4 7 9|8 5 1|6 2 3|
|5 2 8|6 7 3|4 1 9|
|6 1 3|2 4 9|8 7 5|
++++++++++++
|2 8 4|5 6 7|3 9 1|
|7 3 1|9 2 8|5 6 4|
|9 6 5|3 1 4|2 8 7|
++++++++++++

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