Puzzimo

How to solve Jigsaw Sudoku: reading the shapes

5 min read ·

Jigsaw Sudoku replaces the familiar 3×3 boxes with nine irregular regions, each still holding nine cells. Rows and columns work exactly as before; it's the regions that change, and with them the places where a digit can hide.

The good news: odd shapes are often easier to read than square boxes, once you know what to look for. This guide shows how.

The rules

  • Every row and column contains 1 to 9 exactly once.
  • Every coloured region of nine cells contains 1 to 9 exactly once.
  • The regions change from puzzle to puzzle; each one is connected and has nine cells.
The regions are irregular, but each holds exactly nine cells and every digit from 1 to 9 once.

The basics (scanning, singles, notes and pairs) are the same as in classic Sudoku, and our Sudoku guide covers them in detail.

How to solve Sudoku

Scan each region like a box

Scanning works region by region: pick a digit missing from a region, then look along every row and column that passes through it. Because a region can span four or five rows, a single digit outside it can rule out cells in several places at once.

Cells that poke out

The most useful feature of a jigsaw grid is the cell that sticks out of its region into a neighbouring row or column. Look at a row: most of its cells may belong to one or two regions, with a single cell belonging to a region that mostly sits elsewhere.

  • If a region has all but one of its candidates for a digit in one row, the last one is the only place left outside that row.
  • If a region lies entirely within a few rows except for one cell, that cell often decides what those rows still need.

The rule of 45 with regions

Every row, column and region holds 1 to 9, so each adds up to 45. That gives a classic jigsaw trick: compare whole rows with whole regions.

  1. Pick a band of rows, say rows 1 to 3. Together they hold three of each digit.
  2. Find the regions that lie almost entirely in that band. Most of their cells are inside it; a few stick out, and a few band cells belong to other regions.
  3. The cells that stick out and the cells that stick in must hold the same digits, because both sides contain three full sets of 1 to 9.

When only one cell sticks out and one sticks in, they must hold the same digit. That single fact often unlocks a hard jigsaw.

A solving routine

  1. Scan every region for each digit, then every row and column.
  2. Look for regions with cells poking into other rows or columns.
  3. Apply the rule of 45 to bands of rows or columns and the regions inside them.
  4. Write notes and look for pairs inside regions as well as rows and columns.

Practise on the right level

Puzzimo's Jigsaw Sudoku has three levels: Easy gives about 38 digits, Medium about 31 and Hard about 26, and every puzzle has exactly one solution. Notes, undo and hints are built in (a hint adds 30 seconds to a ranked time); a wrong digit counts as a mistake, and the third ends the round.

Play Jigsaw Sudoku now

Frequently asked questions

Is Jigsaw Sudoku harder than regular Sudoku?

It feels different more than harder. Irregular regions make some deductions harder to see, but the cells where regions poke into other rows give you extra clues that square boxes never do.

Do the regions always have nine cells?

Yes. Every region has exactly nine connected cells and contains each digit from 1 to 9 once, just like a box in classic Sudoku.

What is the rule of 45 in Jigsaw Sudoku?

Every row, column and region adds up to 45. Comparing a group of whole rows with the regions that almost fill it tells you that the cells sticking out and the cells sticking in hold the same digits.