Odd/Even Sudoku
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4
9
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7
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Mistakes
0/3
Score
-
Time
00:00
Progress0%
Odd
Even
Easy · Odd/Even Sudoku
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How to play Odd/Even Sudoku
Standard Sudoku rules apply. Purple-ringed cells (odd) must contain 1, 3, 5, 7, or 9. Yellow cells (even) must contain 2, 4, 6, or 8. A wrong parity digit counts as a mistake.
Full guide →
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
What is Odd/Even Sudoku?
Odd/Even Sudoku is a variant where some cells are shaded to indicate whether they must hold an odd or even digit. Purple-ringed cells must hold odd digits (1, 3, 5, 7, or 9). Yellow-shaded cells must hold even digits (2, 4, 6, or 8). Standard Sudoku rules apply to all cells.
What is parity in Sudoku?
Parity refers to whether a number is odd or even. In Odd/Even Sudoku, you can immediately halve the candidate list for any shaded cell. An odd cell can only hold 1, 3, 5, 7, or 9. An even cell can only hold 2, 4, 6, or 8. Combined with row, column, and box constraints, parity constraints make early placements much faster.
How do parity markings help solving?
Shaded cells eliminate half the digit range immediately. If a row already contains three odd digits and has an odd-marked cell remaining, that cell is heavily constrained. Counting odd vs even cells in each row, column, and box often reveals hidden singles that would be invisible without the parity markings.
Is Odd/Even Sudoku harder than regular Sudoku?
At easy and medium difficulty, it is comparable to or easier than classic Sudoku because parity markings provide immediate candidate reductions. Hard and expert Odd/Even puzzles use sparser markings and fewer given digits, making them comparable in difficulty to hard classic Sudoku.
What is the best first move in Odd/Even Sudoku?
Scan each row, column, and box and count how many odd and even slots remain versus how many odd and even digits are still unplaced. When only one cell in a row can hold an odd digit, that cell must contain an odd digit from the remaining candidates — this is a parity-based hidden single.
How long does Odd/Even Sudoku take to solve?
Easy puzzles take 5–15 minutes. Medium puzzles run 15–30 minutes. Hard puzzles average 30–60 minutes and expert puzzles can take 60–90 minutes. Parity-based hidden singles are the primary acceleration technique that distinguishes fast solvers.