Playing sudoku is addictive, and you can never have enough puzzles. When you become a skilled player, you may want more challenging puzzles and try a different and more difficult type. You may have solved a lot of classic sudokus that are very common in all sudoku books or online sites. However, a variation that is perfect for more skilled and experienced players is jigsaw sudoku online. It is also popularly known as irregular sudoku. This type of sudoku is considered challenging and addictive as compared to other variations. Let’s find out why.
How do you solve a jigsaw Sudoku?
In jigsaw sudoku, the rules are very simple, as the rules for standard sudoku still apply. Each row and column must contain numbers 1 to 9 exactly once. However, jigsaw sudoku online is generally trickier to solve than standard sudoku. Why? Because instead of a 3×3 square/region, in jigsaw sudoku, you will see irregular jigsaw-like shapes. These jigsaw-like shapes must also contain the numbers 1 to 9 exactly once. It is harder for our naked eye to work with the wiggly, irregular-shaped regions that replace the orderly 3×3 boxes in standard sudoku puzzles. This makes jigsaw sudoku puzzles more difficult to solve. We often miss deductions that we would spot easily if the grid had its more familiar shape as with regular sudoku grids.
One of the most enjoyable elements about jigsaw sudoku 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. Also, many of these have a unique character of their own dictated by their geometry: whereas every sudoku grid is the same in regular sudoku, the pattern of jigsaw sudoku varies from puzzle to puzzle and can have a large impact on how the puzzle solves. Because of the irregular-shaped nature of the regions, it is easy to see how the puzzle got its name, jigsaw sudoku. Let’s try solving a sample jigsaw/irregular sudoku.
The sample above is jigsaw sudoku. As mentioned previously, the rules of normal sudoku are applicable. In this discussion, let’s just focus on how these irregular-shaped regions will help you solve it easier and faster. I named the 9 regions for easier reference in explaining the sample solutions stated below.
1. We can see that in region 7, number 4 can easily be solved. Since 4 is in columns 1 and 2, it gives us Row 7 Column 3 (R7C2) as the locked cell for number 4. See the text and lines highlighted in green in the figure below.
2. The key to solving jigsaw sudoku is of course to make the most of the shapes of the regions. In column 7, since 5 is already given in Region 6, it will leave us only two possible cells for number 5 in column 7: R4C7 and R8C7. However, in R8C7, since this cell belongs to region 8 and it already has the number 5, R8C7 cannot have a 5. Therefore, the only possible cell for number 5 in column 7 is R4C7 using the region intersection elimination. See the text and lines highlighted in blue in the figure below.
3. Focusing on region 9, number 9 is already given in column 9, therefore, it leaves us R7C8, R8C8, and R9C8 as the possible cells for number 9 in region 9. Using the sudoku techniques you learned before since 9 is already given in Rows 7 and 9, R8C8 is the automatic cell for number 9 in region 9. See the text and symbols highlighted in yellow in the figure below.
Also, at the start of the puzzle, take a good look at the shape of the jigsaw regions and see if you can spot any jigsaw regions that share many of their squares with a row or column, as this can often bear fruit quickly by reducing possible locations for any of its givens in that shared region.
With these sample strategies, try to finish this puzzle. There are more free jigsaw sudoku online puzzles available that you can use in practicing this type of sudoku.