4/6/2023 0 Comments Rules of sudoku![]() ![]() So the four green squares outside the sandwich region sum to 45-11-10 = 24. Now, we know that the digits between 1 and 9 sum to 11. ![]() We have also marked the squares outside of the 1 and 9 sandwich in green: However, where this becomes useful is when we know where the 1 and 9 are in a region that doesn't use every square in a row or column, and we can therefore use it to restrict the value of digits outside the 1 and 9 sandwich region.įor instance, look at the grid position below, where we have placed the 1 in row six of the grid. For instance, trivially in the grid above, since we know the red squares sum to 35, then the squares containing 1 and 9 must sum to 10 (45-10). Remember that since the number outside a row or column is the total between the 1 and 9 in that region, then the squares outside of the 1 and 9 must sum to 45 minus that number. Since 35 must be made from seven squares, and we have nine in any row or column, then we know that the 1 and 9 must be placed in the first and last squares in the column, and thus we can pencilmark those with 1 and 9 accordingly, and mark the rest of the column in red to indicate it can't contain 1 and 9, like this: Now look at column one of the example grid at the top of this page (which is the 9x9 sample puzzle you can play via the link above). In a 9x9 grid, the greatest total around the outside that is possible is 35, because that's the sum of the digits 2 through to 8. By working out which squares can and cannot contain the 1 and 9 in each row and column, you will gradually be able to make deductions. Press the same colour again to turn the square white again. You may find it useful to mark squares that cannot contain the high and low digits in some way, for instance with the online player you can mark a square red by highlighting the square then pressing the red colour box. When you start solving a sandwich sudoku, it is useful to look at each row and column and try to work out where the 1 and 9 (or 1 and 6 in a 6圆 puzzle) can be placed. No guessing is ever required, just careful thinking. Strategy and Solving Tips for Sandwich SudokuĪll our sandwich sudoku puzzles can be solved using logic, and have a single, unique solution. If you enjoy this puzzle type, you can join our online Puzzle Connoisseur's Club for £12 or $17 a year and play a new Sandwich Sudoku Puzzle puzzle every day of the year, together with many other fun and interesting logic puzzles.
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