Jigsaw Sudoku

Jigsaw Sudoku (also called Irregular, Geometric, or Nonomino Sudoku) keeps everything you know about classic Sudoku and changes one thing: the boxes. Instead of nine tidy 3x3 squares, the grid is carved into nine irregular jigsaw-shaped regions.

The Rules

Jigsaw Sudoku follows the familiar Sudoku logic, with the box constraint reshaped:

• Every row must contain the digits 1-9 with no repeats.
• Every column must contain the digits 1-9 with no repeats.
• Each of the nine irregular regions must contain the digits 1-9 with no repeats.
• There are no 3x3 boxes. The bold outlines mark the region each cell belongs to.

How to Solve It

The solving techniques are the same as classic Sudoku — scanning, naked singles, hidden singles — but you apply them to the irregular regions instead of square boxes. Watch the region shapes carefully, since a region can stretch across several rows and columns.

A handy trick carries over from classic play: because every row, column, and region holds 1-9, any line of cells that exactly covers a set of full regions sums to a known total. Comparing a region against the rows or columns it overlaps often pins down a forced digit.