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Introduction Solving Puzzles |
Sudoku /
Sudoku Conventions Quantity of GivensSudoku Puzzles begin with usually about one third of the Cells filled in with Givens. Numbers appear as Givens as often as five times, but rarely more. It is usual for every Number to appear as a Given at least once, although occasionally one Number will not appear. The example shown here† has 26 Givens. The Number 2 appears five times and Numbers 1, 7 and 9 each appear only once. Note that the difficulty of the Puzzle depends much more on the arrangement of Givens rather than how many of them there are. Symmetry in the Positions of GivensJust as crossword puzzles by convention show symmetry in the arrangement of black and white squares, Sudoku puzzles are usually symmetrical in the placement of Givens. The most common form is 2-fold rotational symmetry (also known as 180° rotational, two-way or half-turn symmetry). This is illustrated by the example above. The original puzzle, as it appeared in the newspaper, is shown at left, but background colors have been added to help you keep track. At right, the puzzle image has simply been rotated by 180° in the editor (Microsoft Paint). The pattern of Givens (with green backgrounds) is identical. † The puzzle used as an example appeared in the Boston Globe newspaper on Thursday, November 10th, 2022. It is rated by the Globe as “more difficult”.
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