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These pages demonstrate The Negative Sudoku Dot System, a strategy for solving many Sudoku puzzles, and for getting a good start on even the toughest of puzzles.
Each dot in this system represents a number that cannot be in that cell. The dots are arranged like a push-button telephone: one is in the upper-left, five is in the middle, eight is in the bottom-middle, etc.
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For example, The dots in this cell indicate that two, three, five, seven, and nine cannot be the value in this cell. |
No dots need to be erased as you are solving the puzzle. This is an advantage over other strategies (like the 'pencil notes' strategy) in which the dots (or numbers) in each cell must be erased and rewritten each time a cell is filled.
The Negative Sudoku Dot System will solve
While it will solve all easy puzzles, it is overkill to use this strategy for anything but hard (and harder) puzzles. This strategy, however, is invaluable for getting a good start on even the hardest of puzzles. You may reach a point where no more values can be determined. You will then need to use advanced strategies (such as various wing, pair, coloring, guardian, and rectangle techniques) to fill in subsequent cells. After each value is discovered, however, The Negative Sudoku Dot System may be used once again to continue filling in the rest of the puzzle.
As with any dot system, there are two main disadvantages with The Negative Sudoku Dot System. First, it is tedious, and, second, the dots can become cluttered and confusing. As stated above, because it is tedious, it is wasteful to use this system on easier puzzles.
Regarding cluttered dots, if you make the dots too big, or don't align them with care, you will become confused. Make them as small as you are comfortable (consider a mechanical pencil), and be as neat as you can. In particular, put the dot for number five in the dead center of the cell.
Finally, while you are getting used to the system, you will inevitably forget a dot here or there. It is critical when you get particularly stuck, to 'redot' the entire puzzle. Don't erase anything, just go through each cell and verify that all dots are correct. It is not unusual to catch a mistake here or there.
While this tutorial presents the Negative Sudoku Dot System pretty strictly, there's no need to be so rigid once you become comfortable with it. You don't have to follow these steps exactly, it's just the easiest way to present the information.
Click on the puzzle to proceed.
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