XV Sudoku
X between cells means they sum to 10; V means they sum to 5
What is XV Sudoku?
XV Sudoku (also called Ten-Five Sudoku) places X and V markers between adjacent cells. An X means the two cells sum to 10; a V means they sum to 5. Many XV puzzles use the negative constraint: the absence of a marker guarantees the pair neither sums to 10 nor to 5. Combined with standard Sudoku, this provides very tight constraints across the grid.
At a Glance
| Constraint type | Cell Relationships |
| Typical givens | 18–24 |
| Difficulty rating | ★★★☆☆ 3/5 |
| Avg. solve time — Easy | 8 min |
| Avg. solve time — Medium | 18 min |
| Avg. solve time — Hard | 35 min |
| Avg. solve time — Expert | 62 min |
How to Solve XV Sudoku
| Technique | What it does | 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 Times
Easy
8 min
Medium
18 min
Hard
35 min
Expert
62 min
Frequently Asked Questions
What digit pairs sum to 10?
Only (1,9), (2,8), (3,7), and (4,6). The digit 5 cannot appear in an X pair.
What digit pairs sum to 5?
Only (1,4) and (2,3). The digit 5 cannot be in any V pair within the 1–9 range.
Is the negative constraint always applied?
Yes — our XV Sudoku uses the negative constraint: no X or V means neither condition holds.