Palindrome Sudoku

Palindrome Sudoku is a variant of standard Sudoku that adds one or more designated lines to the 9×9 grid. Along each marked line, the sequence of digits must read identically in both directions, meaning the digit at one end must match the digit at the opposite end. This palindrome constraint applies in addition to the standard Sudoku rules of each digit appearing once per row, column, and box.

To solve a Palindrome Sudoku, you apply standard Sudoku rules while also ensuring that digits along any marked palindrome line mirror each other from end to end. For example, if a line has five cells, the first and fifth must contain the same digit, as must the second and fourth. This symmetry creates additional logical constraints that can help eliminate candidates.

Palindrome Sudoku puzzles appear in various Sudoku variant collections, both in print and on websites dedicated to puzzle variants. Some online puzzle communities and competitive Sudoku platforms feature palindrome variants regularly. They are also common in World Sudoku Championship competitions as a variant round.

Yes, there are many Sudoku variants that add line-based constraints similar to Palindrome Sudoku, such as Anti-Knight, X-Sudoku (diagonal), and Killer Sudoku. Another closely related variant is 'Thermometer Sudoku,' where digits along a marked line must increase from the bulb. These variants are popular in competitive Sudoku solving.