Diagonal Sudoku (X-Sudoku)

Add two more no-repeat units across the main diagonals.

Rules

Each row, column and 3 by 3 box contains 1 through 9 once. In the usual X-Sudoku form, each of the two marked main diagonals must also contain 1 through 9 once. Follow the markings: ordinary Sudoku does not impose diagonal rules.

A visual example

Diagonal Sudoku (X-Sudoku) example diagram — The diagram marks both diagonals. The center cell belongs to both, so a digit already used anywhere on either diagonal is excluded from the center, as well as digits in its row, column and box.

How to start

Treat each marked diagonal as another nine-cell unit. Track its missing digits and look for hidden singles or pairs. If eight cells on a diagonal contain 1 through 8, the ninth is 9; still check the rest of the grid for earlier mistakes.

A mistake to avoid

Only the specified diagonals are extra units. Short parallel diagonal lines do not gain a no-repeat rule merely because the puzzle is called diagonal Sudoku.

Keep learning

Review the standard rules and worked solving techniques. Our daily game and printable packs use standard Sudoku rules; they do not play this variant.