Best SudokuSudoku X
Sudoku X, also called Diagonal Sudoku, is classic Sudoku with one extra rule: both long diagonals must also hold every digit from 1 to 9 exactly once. It’s an easy way into variants, because the extra rule is simple and gives you more places to look for singles.
The rules
- Fill the grid so every row, column and 3×3 box holds 1 to 9.
- Both main diagonals (shaded) must also hold 1 to 9 with no repeats.
An example puzzle
An Easy Sudoku X puzzle with 19 starting digits. It has one solution.
Solving tips
- Treat each diagonal as a fourth kind of row. A number that can only go in one cell of a diagonal is a hidden single, just like in a row.
- The centre cell sits on both diagonals, so it sees more cells than any other. Start there.
- A digit already on a diagonal can’t appear again on it, which clears candidates in all the diagonal’s other cells.
- Corner cells are on one diagonal and in one box, row and column each. Check them with all four groups at once.
What changes from classic Sudoku
Nothing about rows, columns and boxes changes. The diagonals only add rules, so every technique you know still works, and the extra rule often turns a hard step into an easy one.