Odd / Even Sudoku
Shaded cells must contain odd digits; circles must contain even digits
Easy
Odd / Even Sudoku Easy
Medium
Odd / Even Sudoku Medium
Hard
Odd / Even Sudoku Hard
Expert
Odd / Even Sudoku Expert
What is Odd / Even Sudoku?
Odd/Even Sudoku marks certain cells as odd (often shaded grey) or even (often circled). Odd cells must contain one of 1, 3, 5, 7, 9 and even cells must contain one of 2, 4, 6, 8. This halves the candidate set for marked cells immediately, creating powerful restrictions without providing specific digits.
At a Glance
| Constraint type | Cell Relationships |
| Typical givens | 20–26 |
| Difficulty rating | ★★★☆☆ 3/5 |
| Avg. solve time — Easy | 6 min |
| Avg. solve time — Medium | 14 min |
| Avg. solve time — Hard | 28 min |
| Avg. solve time — Expert | 50 min |
How to Solve Odd / Even Sudoku
| Technique | What it does | Level |
|---|---|---|
| Immediate Candidate Halving | Marked cells instantly reduce to 5 odd candidates (1,3,5,7,9) or 4 even candidates (2,4,6,8). Apply this before any other technique. | Beginner |
| Parity Counting per Box | Count how many odd-marked and even-marked cells are in each box to verify the digit distribution is achievable. | Intermediate |
| Parity-Chain Elimination | If a row must contain exactly four even digits, and three positions are already even-marked, the fourth must come from the remaining unmarked cells. | Intermediate |
| Parity X-Wing | When parity restricts a digit to exactly two rows and two columns, form a parity-based X-Wing for cross-elimination. | Advanced |
Average Solve Times
Easy
6 min
Medium
14 min
Hard
28 min
Expert
50 min
Frequently Asked Questions
How are cells marked?
Shaded grey cells must contain an odd digit (1, 3, 5, 7, or 9). Circled cells must contain an even digit (2, 4, 6, or 8).
Can an unmarked cell contain any digit?
Yes — unmarked cells have no parity restriction beyond standard Sudoku rules.
Does the digit 5 count as odd?
Yes — 5 is odd and can appear in a shaded cell.