Place the numbers from 1-9 once in each row, column and bold-lined jigsaw region
Here is an image of the start position of a jigsaw sudoku puzzle:
The rules of jigsaw sudoku are very simple, as with standard sudoku itself. However, jigsaw sudoku are generally trickier to solve than standard sudoku. This is partly because it is harder for the human eye to work with the wiggly, irregular-shaped regions that replace the orderly 3x3 boxes in standard sudoku puzzles. We often miss deductions that we would spot easily if the grid had its more familiar shape as per regular sudoku grids.
The beauty of jigsaw sudoku is that there are a huge range of different grid patterns possible, and many of these have a unique character of their own dictated by their geometry: whereas every sudoku grid is exactly the same, the pattern of a 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. It is also known as jigsawdoku, irregular sudoku and no doubt has various other names too. It is one of the more commonly seen sudoku variants that exist.
Strategy and Solving Tips for Jigsaw Sudoku Puzzles
Here are a few strategy tips to help you solve these puzzles:
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.
You will often need to follow through the implications of what you spot to make progress. For instance, in the example grid, there is a given 3 at the bottom-left of the grid in the pink region. This pink region shares fully five of its squares with column one. That restricts the 3 in column 1 to one of the four squares in the green region at the top-left of the grid. This in turn means none of the other squares in that light-green region can contain a 3. This restricts where the 3 can go in column 4 to only two places (its 5th and 6th squares) and so we should pencilmark that accordingly.
As with standard sudoku, have a quick look through for the numbers that occur most frequently in the start position and see if you can make any instant progress as a result. In the example grid, six of the nine 7s are already given to you. This can be used to make instant progress: look at column 4, there is only one square that can contain the 7, can you see where? This then pins down the location of the 7 in column 7, and then there is only one possible place for the 7 in column 1, and that is all the 7s placed in the grid!
This video walks through the solve of the puzzle above using the strategies outlined above and more, so, if you've not already done so, you might like to give it a go before watching this video: