Palindrome Sudoku
2
9
7
3
5
5
1
2
9
4
1
8
9
2
7
4
2
5
3
3
2
9
5
9
8
3
6
4
9
6
2
4
1
9
4
3
5
2
How to play Palindrome Sudoku
Standard Sudoku rules apply. Each grey line is a palindrome - The sequence of digits reads the same from both ends. For a 5-cell line reading 3,7,5,7,3, position 1 = position 5 and position 2 = position 4.
Full guide →
The digit sequence along a line reads the same forwards and backwards
Easy
Palindrome Sudoku Easy
Medium
Palindrome Sudoku Medium
Hard
Palindrome Sudoku Hard
Expert
Palindrome Sudoku Expert
What is Palindrome Sudoku?
Palindrome Sudoku marks lines on the grid whose digit sequence must be a palindrome — reading the same in both directions. If a line has cells A-B-C-D-E, then A=E and B=D, while C is the central digit. This creates pairs of cells that must share the same value, acting as powerful equality constraints across the grid.
At a Glance
| Constraint type | Line Constraints |
| Typical givens | 20–28 |
| Difficulty rating | ★★★☆☆ 3/5 |
| Avg. solve time — Easy | 7 min |
| Avg. solve time — Medium | 16 min |
| Avg. solve time — Hard | 32 min |
| Avg. solve time — Expert | 58 min |
How to Solve Palindrome Sudoku
| Technique | What it does | Level |
|---|---|---|
| Mirror Pair Identification | In a palindrome of length L, cell i and cell L+1−i must share the same digit. Identify all mirror pairs before solving. | Beginner |
| Centre Cell Freedom | The central cell of an odd-length palindrome has no mirror constraint — it is only restricted by standard row/column/box rules. | Beginner |
| Mirror Propagation | Once one cell of a mirror pair is determined, immediately set its partner to the same value. | Intermediate |
| Multi-Palindrome Intersection | If two palindromes share a cell, that cell must satisfy both palindrome relationships simultaneously. | Advanced |
Average Solve Times
Easy
7 min
Medium
16 min
Hard
32 min
Expert
58 min
Frequently Asked Questions
What is Palindrome Sudoku?
Palindrome Sudoku is a variant where grey lines are drawn across the grid. Every grey line must read the same forwards and backwards — meaning the first cell mirrors the last, the second mirrors the second-to-last, and so on. Standard Sudoku rules apply throughout.
How does the palindrome constraint work?
For any palindrome line, cell positions are mirrored around the centre. On a 6-cell line, cells 1 and 6 hold the same digit, cells 2 and 5 hold the same digit, and cells 3 and 4 hold the same digit. This immediately links distant parts of the grid — placing a digit at one end fixes the digit at the other end.
Can palindrome lines have repeated digits?
Yes, palindrome lines inherently require digit repetition — each mirrored pair shares the same digit. However, standard Sudoku rules still apply, so a repeated digit must be in different rows, columns, and boxes. Palindrome lines are carefully constructed so that this repetition is always consistent with uniqueness rules.
Is Palindrome Sudoku harder than regular Sudoku?
Easy palindrome puzzles are often easier than classic Sudoku because the mirroring immediately links cells across the board, providing extra deductions. Harder difficulties become quite challenging because you must track mirrored constraints across long lines while maintaining standard Sudoku logic.
What is the best first move in Palindrome Sudoku?
Find palindrome lines where one endpoint cell is already constrained by its row, column, or box. Placing a digit there immediately fixes the mirrored cell at the other end. Also look for odd-length lines — the centre cell has no mirror partner, so it's only constrained by standard Sudoku rules.
How long does Palindrome Sudoku take to solve?
Easy puzzles take 8–15 minutes. Medium puzzles run 15–30 minutes. Hard puzzles average 30–60 minutes and expert puzzles often exceed 90 minutes. The difficulty increases sharply when multiple long palindrome lines overlap across the same region of the grid.