Jigsaw Sudoku

In Jigsaw Sudoku (also called irregular Sudoku) the familiar 3×3 boxes are replaced by nine irregular regions of nine cells, outlined with thick borders. Each row, each column and each region must contain the digits 1 to 9 exactly once.

Because the regions are different every game, techniques that rely on the box shape stop working automatically — you have to look at each region afresh. Every layout is generated, filled and checked for a unique solution.

1. Select a cell and enter a digit.
2. Every row, column and outlined region contains 1–9 once.
3. Use Notes for candidates and Hint if you are stuck.

• Look where regions cross rows. A region that pokes one cell into a row can force that digit.
• Use the 45 rule on lines. Adding up whole regions that almost cover a set of rows shows which digits the leftover cells must hold.
• Scan region by region for hidden singles before moving on to rows and columns.