All Sudoku Variants
9×9 · Irregular Region

Jigsaw Sudoku

Also known as Irregular Sudoku, Nonomino Sudoku, Squiggly Sudoku

The 3×3 boxes are replaced by nine irregular nine-cell regions; row, column and region rules otherwise unchanged.

1 6 5 4 9

An example Jigsaw Sudoku: the nine 3×3 boxes are replaced by irregular colour-coded regions, each of which still holds 1–9.

Jigsaw Sudoku keeps almost everything about the classic puzzle and changes one thing: the nine 3×3 boxes are replaced by nine irregular, jigsaw-shaped regions. Every row and column still holds the digits 1–9 once, and now each jagged region must too. That single twist makes the grid feel completely different to solve, because the neat box logic you rely on in Classic Sudoku no longer lines up with the rows and columns.

The rule: rows, columns, and jagged regions

The regions are drawn as connected blobs of nine cells with heavy borders, and they tile the grid with no gaps or overlaps. Fill the grid so that each of the nine rows, each of the nine columns, and each of the nine regions contains 1–9 exactly once. Below is a smaller 6×6 example — the digits run 1–6 — so you can see how the regions wander across the grid instead of sitting in tidy blocks.

Six irregular regions replace the boxes. Each colour is one region, and each must hold 1–6 — just like every row and column.

Why one jagged region still holds every digit

It is easy to forget, mid-solve, that a twisty region works exactly like a box: it is a group of cells that must contain each digit once. The green region below snakes through two rows, yet it still holds 1 through 6 with no repeats — no different, logically, from a 3×3 box holding 1 through 9.

1 2 3 4 5 6

The green region winds across two rows but still contains 1–6 exactly once — a box in disguise.

What changes compared with Classic

Two familiar things behave differently. First, box-line interactions vanish: pointing pairs and box/line reduction rely on a box aligning with a row or column, and jigsaw regions rarely do. Second, and more usefully, a region can share many cells with a single row or column, which opens a technique that barely exists in Classic Sudoku — the law of leftovers.

The law of leftovers

Because rows, columns and regions all contain the same nine digits, you can compare a block of rows (or columns) against the regions that cover it. Say two full rows — eighteen cells — are almost exactly covered by two regions, except that the regions poke out into a few extra cells and leave a few row cells uncovered. The "leftover" cells sticking out of the block must contain the very same digits as the uncovered cells inside it, because both sets make up the difference between "two rows" and "two regions", and both must total the same nine-digit content. This single idea resolves cells that no ordinary scan would touch, and it is the signature move of Jigsaw solving.

Solving strategy

  • Hunt the small overlaps first. Where a region dips just one or two cells into a row or column, those cells are tightly constrained — often an immediate hidden single.
  • Use the law of leftovers early. Pairs of rows or columns against their covering regions frequently hand you two or three digits at once.
  • Watch the fat regions. A region that stretches across five or six rows touches many units and tends to resolve last, so pencil it carefully.
  • Drop the box habits. Pointing pairs and box/line reduction mostly won't fire — lean on row, column and region scanning instead.

Common mistakes

  • Treating a region like a box. Regions are not 3×3 and rarely align with the grid lines — a digit "seen" across a box boundary in Classic may be perfectly legal here.
  • Forgetting rows and columns still apply. The jagged regions are an addition to the row and column rules, not a replacement.
  • Miscounting a region. Regions wind and double back; always confirm a region truly has nine cells before reasoning about which digits it still needs.
  • Skipping the law of leftovers. Solvers who only scan single units stall on exactly the deductions this technique is built to crack.

Can I play it here?

Not yet — Jigsaw Sudoku isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile: