Hard XV Sudoku

X marks cells that sum to 10; V marks cells that sum to 5. All unmarked adjacent pairs must not sum to 5 or 10.

Easy Medium Hard Expert

Hard XV Sudoku. Dense XV networks demand chaining positive and negative pair constraints across the full board before individual digits resolve.

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

What is XV Sudoku?

Difficulty
★★★☆☆
3/5
Constraint Type
Cell Relationships
Typical Givens
18–24
Avg. Solve (Hard)
35 min

Solving Techniques for Hard Level

Technique Description Level
Negative Constraint Where no X or V appears between adjacent cells, their sum is neither 10 nor 5. This eliminates (1,9), (2,8), (3,7), (4,6) for X and (1,4), (2,3) for V. Beginner
Sum Pair Enumeration List all digit pairs that sum to 10 (for X) or 5 (for V), then use row/column placement to identify which pair must occupy each marked pair. Beginner
Marker Chain Logic Multiple consecutive X and V markers in a row form a sum chain — enumerate valid assignments for the entire chain simultaneously. Intermediate
Box X-Interaction An X pair forces both digits into specific positions within their shared box, constraining all remaining cells of that box. Advanced

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Average Solve Time by Difficulty

Easy
8 min
Medium
18 min
Hard
35 min
Expert
62 min
Want a full walkthrough of rules, strategies, and solving steps? How to Play XV Sudoku →

Frequently Asked Questions — Hard XV Sudoku

What makes hard XV Sudoku difficult?
Hard XV Sudoku has a dense network of X and V markers combined with many unmarked pairs, all of which carry negative constraints. Resolving the puzzle requires tracking positive constraints (X and V sums) and negative constraints (non-X, non-V pairs) simultaneously across many cells, which creates long deduction chains before individual digits can be placed.
How do I use XV chains to solve hard puzzles?
An XV chain links two or more marked pairs in sequence. If cell A has an X with cell B (summing to 10) and cell B has a V with cell C (summing to 5), and cell A is confirmed as 3, then B must be 7 (from the X), and C must be unable to pair with 7 in a V (since 7+V would need -2). Tracing these chains through marked cells is the main hard-level technique.
Should I use pencil marks for hard XV Sudoku?
Yes. For hard puzzles, track both standard Sudoku candidates and the XV pair constraints in your notes. Mark which cells are part of X pairs and which are part of V pairs, and cross-reference with the negative constraint. Without written marks, the volume of inter-cell relationships becomes too large to hold in working memory.
How do naked pairs interact with XV constraints in hard puzzles?
A naked pair in a row or column eliminates two digits from all other cells in that unit. If one of those cells is part of an X or V pair, removing a digit may force the paired cell into a specific value, propagating the deduction further. Always update XV pair implications whenever a naked pair fires.
How long does a hard XV Sudoku take to solve?
Expect 30 to 55 minutes on hard XV puzzles. If you are stalled, check every unmarked adjacent pair in the most constrained row or column and apply the negative constraint. This single step most often breaks a deadlock in hard XV Sudoku.

More questions? See the full XV Sudoku guide.