Expert 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

Expert XV Sudoku. XV forcing chains and exhaustive negative-constraint analysis — the hardest pair-sum puzzles on the site.

7
5
1
9
4
1
3
9
3
2
6
4
9
1
1
2
2
8
9
8
4
7
6
V X V X V V V X X V V X V V V V V X X X X X X
Mistakes
0/3
Score
-
Time
00:00
All XV Sudoku Puzzles →
Progress0%

What is XV Sudoku?

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

Solving Techniques for Expert 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

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 — Expert XV Sudoku

Is expert XV Sudoku solvable without guessing?
Yes. Every expert puzzle on Sudoku.by has a unique solution reachable purely by logic. Expert XV Sudoku chains together many positive and negative constraints into long deduction sequences. If you feel compelled to guess, a constraint interaction involving the negative XV rule (unmarked pairs) has almost certainly been overlooked.
What advanced techniques appear in expert XV Sudoku?
Expert XV Sudoku requires XV forcing chains (assuming a cell value and tracing its XV consequences to a contradiction or confirmation), hidden quads within the restricted digit sets that X and V markers create, and subset analysis of which digits can possibly fill a row or column given all positive and negative XV constraints simultaneously.
How do expert XV puzzles differ from hard XV puzzles?
Expert puzzles provide fewer initial given digits and arrange the X and V markers so that no short chain resolves a cell directly. Every deduction requires tracing multiple XV relationships before a single digit can be confirmed. The negative constraint becomes as important as the positive markers for making progress.
What is the hardest type of deduction in expert XV Sudoku?
The most challenging deductions involve a cell that is unmarked (no X or V) with all eight of its possible neighbours. You must enumerate which digit pairs are forbidden due to missing markers and combine those restrictions with row, column, and box rules to show that only one digit survives. This exhaustive negative-constraint analysis is the defining skill of expert XV solving.
How long does an expert XV Sudoku take?
Expert XV puzzles typically take 60 to 100 minutes. Solvers who systematically apply both positive and negative XV constraints together can finish in 50 to 70 minutes. If you are stuck for more than 20 minutes, take each unmarked adjacent pair in the most constrained unit and explicitly confirm that the non-X, non-V rule has been applied to every candidate combination.

More questions? See the full XV Sudoku guide.