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What is Sudoku? |
Sudoku (or Su Doku, depending on which newspaper you read) is a Japanese number puzzle which requires logic rather than arithmetic to solve it. The classic puzzle size is 9×9 squares. To solve a 9×9 puzzle, fill in each square with a number from 1 to 9 in such a way that each row, column and 3×3 square block of the puzzle contains each number only once.
Other sizes of puzzle are solved in exactly the same way, except that 4×4 puzzles use the numbers 1 to 4, 16×16 use the numbers 0 to 9 and letters A to F, and 25×25 use the letters A to Y. 6×6 puzzles use the numbers 1 to 6 and have rectangular blocks rather than square ones.
If you need help in understanding how to approach solving a puzzle, look at the following example of a 9×9 puzzle.
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The two basic methods are as follows: The area-checking method: Look at the top-left block of squares. The numbers 3, 5 and 7 are missing. The 5 cannot go in the left-hand column as there is already a 5 in that column, so it must go in the middle square. We can then see that the 7 must go to its left, as there is already a 7 elsewhere in the third row. Finally the 3 fills in the bottom-left square of the block. The same approach can be used to check a row or column in order to fill in some of its missing values. The single square-checking method: Look at the top-right square in the puzzle. It cannot contain 1 as there is already one in the block. It cannot contain 2, 3 or 4 as they appear in the same column. It cannot contain 6, 7, 8 or 9 as they appear in the same row. It must therefore contain a 5. |
Obviously, once you have filled one square, you will have more information to use to fill further squares in a similar way. Further methods you may find useful for solving more difficult puzzles are outlined in the page on the Solver window.
Samurai puzzles consist of five overlapping 9×9 puzzles in an X formation. Solve each of the five puzzles in the usual way. A block of nine squares from each corner of the central puzzle will also be part of the puzzle at that corner, so the squares in that block have to fit in with two puzzles.
Hidden word puzzles are just like normal 4×4, 6×6, 9×9 or Samurai puzzles except that letters are used instead of numbers, and when the puzzle is complete you will find a word reading across one of the rows or down one of the columns. More details on hidden word puzzles
Killer puzzles have a blank 4×4, 6×6, 9×9 or Samurai grid with areas drawn out in which no value may be repeated and where the values in each area must add up to the total shown. More details on Killer puzzles