An example Palindrome puzzle: cells equidistant from the centre hold equal digits - 3, 7, 5, 7, 3.
Palindrome Sudoku draws grey lines across the grid that read the same forwards and backwards. Along each line, cells the same distance from the two ends hold equal digits - just as a palindrome word like "level" mirrors around its middle. The line itself places no digits, but its mirror symmetry links cells all over the grid.
The rule: mirror around the centre
Fold a palindrome line at its midpoint and the two halves must match: the first cell equals the last, the second equals the second-to-last, and so on. A five-cell line therefore has the pattern a-b-c-b-a. Below, the line reads 3-7-1-7-3 - a genuine palindrome.
A palindrome line reads the same both ways: 3-7-1-7-3. Mirror cells hold equal digits.
Reading the mirror pairs
The power of a palindrome is that it forces distant cells to be equal - the opposite of Sudoku's usual "all different" instinct. Each coloured pair below must hold the same digit. That has an immediate consequence: if two mirror cells ever fall inside the same row, column or box, the line is impossible, because equal digits cannot share a unit. So a palindrome's length and route are tightly limited by where its mirror cells land.
On a six-cell line the mirror pairs (matching colours) must be equal - and so can never share a row, column or box.
How it helps you solve
Every value you place on a palindrome is instantly copied to its mirror, so one deduction does double duty. Better still, the mirror constraint chains: if cell a equals cell e, and cell e is pinned by its row, then cell a is pinned too, perhaps far across the grid. Look for mirror cells that sit in already-crowded units - they often resolve at once and then hand you their partner for free.
Solving strategy
- Copy across the mirror. Any digit placed on the line appears immediately at its mirror position.
- Check for illegal pairs. Mirror cells in the same unit are impossible - use that to rule candidates out.
- Exploit crowded partners. When one mirror cell is heavily constrained, solve it and copy to the other end.
- Feed the grid. Each mirrored placement behaves like two givens for their rows, columns and boxes.
Common mistakes
- Making mirror cells different. The pairs must be equal, not distinct - this is the reverse of the usual Sudoku rule.
- Forgetting the centre. An odd-length line has a lone middle cell that mirrors itself and is otherwise free.
- Allowing a pair in one unit. Equal mirror cells can never sit in the same row, column or box.
- Ignoring the ordinary rules. The palindrome is an extra layer over the usual row, column and box constraints.
Can I play it here?
Not yet - Palindrome Sudoku isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile:
- Browse all the Sudoku variants we do offer.
- Or print free puzzles from the printable PDF page.
Where to play it
Palindrome Sudoku belongs to the constraint family and runs on 9×9. It is not one SudokuStreak generates yet - but the deduction it trains is the deduction every Sudoku runs on.
Difficulty and type are two separate dials here: the type sets the extra rule, the level sets how much of the grid you start with. Expert Sudoku leaves 25 of the 81 cells filled, where the beginner tools dry up almost entirely; Evil Sudoku leaves 23, with no easy moves at all. Take it at the gentler end while the pattern is still new, and move up once it stops being a fight.