Hard Irregular Sudoku

Jigsaw-shaped regions replace the 3×3 boxes. Rows, columns, and irregular regions must each hold 1–9. No download, no login.

Easy Medium Hard Expert

Hard Irregular Sudoku. Complex region shapes with fewer givens — expect pointing pairs across regions, hidden sets, and sustained pencil-mark work.

2
7
9
7
4
1
8
1
6
9
2
7
4
6
2
9
5
7
3
6
4
1
5
8
3
2
5
Mistakes
0/3
Score
-
Time
00:00
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Progress0%

What is Jigsaw Sudoku?

Difficulty
★★★☆☆
3/5
Constraint Type
Irregular Regions
Typical Givens
24–30
Avg. Solve (Hard)
32 min

Solving Techniques for Hard Level

Technique Description Level
Region Identification First Identify all 9 irregular regions by their colour coding before solving. Region membership determines the third constraint unit for each cell. Beginner
Region Counting Each region must contain 1–9. Counting completed rows and columns reveals how many of each digit can still fit in each region. Intermediate
Region–Row/Column Intersection If a digit within a region is confined to one row or column, eliminate it from the rest of that row or column. Intermediate
Irregular Naked Subsets Apply naked pairs and triples within each irregular region exactly as you would within standard 3×3 boxes. Advanced

Ready for the ultimate test? Try Expert Jigsaw Sudoku — the hardest puzzles on Sudoku.by.

Techniques to Master at Hard

  • Hidden Pairs technique — Irregular region geometry hides pairs in cells that share a region but no row or column — deliberately recount candidates region-by-region or you will never see them.
  • X-Wing technique — Rows and columns are unchanged by jigsaw regions, so classic X-Wings still work — and they're often the only move left when region logic stalls in hard puzzles.

Average Solve Time by Difficulty

Easy
7 min
Medium
16 min
Hard
32 min
Expert
60 min
Want a full walkthrough of rules, strategies, and solving steps? How to Play Jigsaw Sudoku →

Related Variants

Irregular Diagonal Sudoku

Your jigsaw region-reading skills plus two diagonal houses — the natural step up in constraint density.

Chaos Construction

Jigsaw solving where the regions themselves are hidden — you deduce the borders while you place the digits.

Samurai Sudoku

Scales the geometry challenge a different way: five overlapping grids whose shared boxes pass information between them.

Frequently Asked Questions — Hard Irregular Sudoku

What makes hard Irregular Sudoku difficult?
Hard puzzles have fewer givens and more complex region shapes that interact with many rows and columns at once. You need pencil marks throughout, and most breakthroughs come from spotting hidden pairs, naked triples, or region-based pointing eliminations that span multiple rows.
What is a pointing pair in Irregular Sudoku?
A pointing pair occurs when a digit within a region can only go in two cells, and both those cells sit in the same row or column. Even though the constraint comes from the region, it eliminates that digit from all other cells in that row or column — just like in standard Sudoku.
Should I use pencil marks for hard Irregular Sudoku?
Absolutely. Hard Jigsaw Sudoku cannot be solved reliably without pencil marks. Fill in all candidates for every empty cell, then systematically eliminate using region, row, and column logic. Without notes, you'll miss multi-cell interactions that are the key to unlocking hard puzzles.
How do irregular regions create unique deduction paths?
Because regions cross row and column lines, a single placement can eliminate a candidate from cells in three different rows, three different columns, and the region all at once. This creates a cascade of eliminations unique to Jigsaw Sudoku and is why hard puzzles unlock dramatically once you find the right move.
How long does a hard Irregular Sudoku take?
Expect 30–50 minutes for hard puzzles. The key bottleneck is usually one or two tricky region-crossing eliminations. Once you find them, the rest of the puzzle often falls into place quickly. Use pencil marks from the start — don't wait until you're stuck.

More questions? See the full Irregular Sudoku guide.