Hard Samurai Sudoku

Five overlapping 9×9 grids share corner boxes. Solve all five simultaneously — each shared box belongs to two grids at once.

Easy Medium Hard Expert

Built on Medium Samurai Sudoku. Fewer givens across all five grids — work sub-grids in parallel and exploit shared boxes for cross-grid deductions.

Score
-
Mistakes
0/3
Time
00:00
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Hard · Samurai Sudoku · 5 sub-grids 0%
How to play Samurai Sudoku
Five overlapping 9x9 Sudoku grids. Each sub-grid must independently satisfy standard Sudoku rules (1-9 in each row, column, and box). Where two sub-grids share a 3x3 corner box, that box must satisfy both grids simultaneously. Solve sub-grids with the most clues first, then use shared boxes to unlock others.
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What is Samurai Sudoku?

Difficulty
★★★★★
5/5
Constraint Type
5 Overlapping Grids
Typical Givens
~30 per sub-grid
Avg. Solve (Hard)
150 min

Solving Techniques for Hard Level

Technique Description Level
Sub-Grid Independence Each of the five 9×9 sub-grids satisfies standard Sudoku rules independently. Solve each one using all standard techniques. Beginner
Overlap Box Exploitation The four corner boxes where sub-grids meet are shared between two grids. Any digit placed in a shared box eliminates that digit from two sub-grids at once. Intermediate
Cross-Grid Cascade Completing a corner box in the central grid forces values in the corresponding corner grid's box, which may cascade further through that grid. Intermediate
Shared Box Forcing When a shared box is nearly complete, use both sub-grids' row and column constraints to force the remaining digits. Advanced
Global Number Counting Across all five sub-grids, each digit 1–9 appears 5×9=45 times total. This global count can confirm placement decisions near the end. Advanced

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Techniques to Master at Hard

  • Hidden Pairs technique — Cross-grid eliminations through shared boxes thin candidates in cells you weren't watching — periodically recount the boxes bordering each overlap, per grid, to catch hidden pairs.
  • X-Wing technique — Fish stay inside a single 9×9 — never build an X-Wing from rows of two different sub-grids — but a fish elimination inside a shared box still exports to the neighbour grid.

Average Solve Time by Difficulty

Easy
45 min
Medium
90 min
Hard
150 min
Expert
240 min
Want a full walkthrough of rules, strategies, and solving steps? How to Play Samurai Sudoku →

Related Variants

Jigsaw Sudoku

A different geometry challenge in one grid — region shapes that snake instead of grids that overlap.

Chaos Construction

For solvers who enjoyed scale, chaos offers depth: deduce the hidden region borders while solving.

Hyper Sudoku

Overlapping regions condensed into a single 9×9 — four windows that share cells with the standard boxes.

Frequently Asked Questions — Hard Samurai Sudoku

What makes hard Samurai Sudoku harder than medium?
Hard puzzles have fewer given digits distributed across five sub-grids, so no single sub-grid is easily solved at the start. You must work multiple sub-grids in parallel, using small deductions from each to incrementally unlock others — a slower, more careful solving rhythm.
How do I handle a Samurai sub-grid that seems completely stuck in hard difficulty?
A stuck sub-grid almost always has a neighbor that can provide the first breakthrough through a shared box. Focus on the adjacent sub-grid and try to determine even one more digit in the shared box — that single placement often triggers a chain back into the stuck grid.
Should I use pencil marks for hard Samurai Sudoku?
Yes, and more systematically than in regular Sudoku. Track candidates for every open cell across all five sub-grids. Shared box cells appear in two sub-grids' rows and columns, so their candidate elimination is doubly constrained and should be prioritized.
What is the hardest type of deduction in hard Samurai Sudoku?
Cross-grid pointing pairs: when a digit's candidates in a shared box are all in the same row of one sub-grid, that digit can be eliminated from the rest of that row in both sub-grids simultaneously. Spotting these cross-grid interactions is the key skill at hard level.
How long does hard Samurai Sudoku take?
Expect 60–120 minutes for hard Samurai Sudoku. The large board and sparse clues make early progress slow. Once the first sub-grid is fully solved, the chain reactions through shared boxes usually accelerate the rest significantly.

More questions? See the full Samurai Sudoku guide.