This enables us to say that R4C5 and R4C6 must be 4 and 8, so we can mark 48,48 as the pencilmarks in those cells. With the 1 in column 5 and the 3 in column 6, this makes the candidates for those cells respectively: 137, 37, 17. This will just leave 1,3,7 which must be placed in cells 4,5,6 in row 6 accordingly. The 5 in row six can also be placed instantly. We can instantly place the '6' in row six using the simple logic above, and it pays dividends taking the time at the start of the puzzle to look for numbers that must go in a particular cell in a row, column or box. You will tend to find that you need to use pencilmarks a lot more with jigsaw sudoku than you do with normal sudoku (unless you are doing a particularly hard sudoku that relies on you going through and noting down each candidate for a particular cell systematically to reduce the options). Looking out at the start of the puzzle for applications of this can be the key to placing values quickly in jigsaw sudoku and making the appropriate eliminations as a result. This only leaves one cell that can contain the 1 in row 1, and that is the final cell, R1C9, and we place it there. This only leaves three cells in row 1 that can contain a 1, but in fact cells 1,2 can't either because there is a 1 placed in R2C2 which contains cells R1C1 and R1C2 in its boundaries. We can see that the '1' in cell Row three Column 5 (R3C5) means that cells 3,4,5,6,7,8 in row one cannot contain a 1. Those that spread across a particularly large number of cells in another region (intersect over those cells) are particularly useful. The key to solving jigsaw sudoku is of course to make the most of the shapes of the regions.

However, there is one rule that you will find yourself using a lot more than in normal sudoku and that is region intersection elimination. The rules that you use in standard sudoku certainly apply, that there is 1 - 9 once in each row, column and in this case irregular shaped thick lined set of nine cells. One of the most enjoyable elements about it is that there are many possible grid types, and therefore each of these presents a different set of regions and therefore a different puzzle each time. This puzzle is one of the more common and more fun of the various sudoku variants. Our Irregular sudoku puzzle magazine, also referred to as Jigsaw Sudoku, has 100 all new irregular sudoku puzzles for you to enjoy.

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