Advanced Sudoku Completion Tricks
In an advanced sudoku puzzle, some of the common tricks, such as hidden pairs and naked quads will only get you so far. To move forward, you need some advanced tricks. Try looking for the X-wing pattern and the swordfish pattern. Once you solve those, the rest of the puzzle maybe as easy as just completing some of the tricks for a beginner puzzle.
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X-Wing Patterns
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Looking for certain patterns can help solve more advanced puzzles. If you are stumped in a challenging puzzle, look for the X-wing pattern. This occurs when two rows (or two columns) each have only two cells where the same number is a candidate.The four spaces where the number is a candidate are diagonally opposite from each other, literally shaped like an X. That number must not be a candidate for any other space in those rows or columns. The number can only go in two of the four positions, per the rules of the game. You won't know yet where the number will go, but all the other spaces in those columns where this number may be a candidate can be eliminated as possibilities. It will only be correct in two of the four X spots.
Sudoku Swordfish Pattern
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Some advanced puzzles may contain the swordfish pattern. This happens when three rows (or three columns) each contain two or three spaces that have a matching candidate. The candidate must be in each of the three rows and share the same three columns.Some of the cells in this pattern may already be solved; that doesn't matter. The number can only be correct in three of the six spaces in this pattern, so the number can be eliminated from anywhere else in the three columns that are not in the swordfish pattern.
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