Matching Sets can be determined by examining the list of Hidden Houses.

Look at the block of N rows (or columns) containing the hidden house - if that hidden house has 5, 6, 7 or 8 cells that are in the same Jigsaw region, then there is a Matching Set of size 4, 3, 2 or 1. There are 4,3,2 or 1 cells in the Jigsaw region that are

outside the N x 9 block, and these correspond to the same number of cells

inside the block that complete the hidden house. (These sets are sometimes called "innies" and "outies").

There are two such instances in the Jigsaw layout above. In each case the set size is 4, and there are 4 cells (marked "A") outside the block whose cell values must match the 4 cells marked "B"):

- MatchedSets.png (6.24 KiB) Viewed 1098 times

Assuming the computer solver knows about the hidden houses, there is little advantage to be gained from implementing Matching Sets checking.

But for P&P solvers, this is normally very useful information!