Jigsaw Sudoku
How to solve Jigsaw Sudoku: the irregular pieces, step by step
Updated Tuesday, October 27
To solve a Jigsaw Sudoku, play it like a classic sudoku with the irregular pieces in place of the 3 by 3 boxes: find the squares that can take only one digit, then the digits that have only one place. Where a piece reaches across a row or a column, the odd shapes give extra clues. Every Gridarium jigsaw sudoku can be solved this way, without guessing.
The rules
Every row, every column and every piece holds the digits 1 to 9 exactly once. The thick lines draw the nine pieces; each has nine squares, but no two have the same shape.
Step 1: the only digit a square can take
Look along a square's row, its column and its piece. If eight different digits are already there, the square can only be the ninth. Easy puzzles need nothing else.
Step 2: the only place for a digit
Pick a digit and a piece (or a row, or a column) that still lacks it. Cross out every square that already sees that digit. When a single square is left, the digit goes there. Medium puzzles need this.
Step 3: where a piece crosses a line
If, inside a piece, a digit can only go in squares of the same row, that digit is locked into the piece's part of the row: no other square of that row can take it. It works the other way round too, from a row or a column into a piece. Irregular pieces make this move come up often, and hard puzzles ask for it.
Step 4: pairs
When two squares of the same row, column or piece can only hold the same two digits, those digits belong to them: cross them out of the other squares of that unit. Hard puzzles sometimes need this.
The three levels
- Easy: 40 digits given; step 1 is enough.
- Medium: 34 digits given; you will need step 2.
- Hard: 28 digits given; steps 3 and sometimes 4 are needed.