Sudoku X
Two diagonals give you more to check
Sudoku X keeps the usual rows, columns and 3×3 boxes, and adds two main corner-to-corner diagonals. Each diagonal also needs the digits 1–9 once. Only cells on those marked lines gain the extra restriction; shorter sloping lines do not.
01
Read each diagonal as a group
List its missing digits, then check their possible positions. One remaining place for a digit is enough for a deduction, even when its row remains open.
02
Check both lines at the centre
The centre belongs to both diagonals as well as its row, column and box. It must satisfy all five groups; it is not automatically 5.
03
Carry the deduction back across
After a diagonal placement, update notes along that diagonal and in the cell’s row, column and box. The extra rule works alongside ordinary Sudoku.