X-Sudoku (Diagonal Sudoku): Rules & How to Solve
Add two diagonals to a classic grid and the whole solve tightens. The friendliest entry point into variants.
The rule
In addition to the normal rules, each of the two main diagonals must also contain the digits 1–9 exactly once.
How to solve diagonal sudoku
Treat diagonals as extra lines
Each diagonal is a ninth region with the same no-repeat rule — scan them just like rows and columns.
The centre cell is powerful
Both diagonals cross the very middle cell, so solving it constrains two lines at once.
Watch box overlaps
A diagonal passes through three boxes; pairing diagonal candidates with box candidates often forces placements.
Frequently asked questions
- What is X-sudoku?
- A sudoku where the two main diagonals must also each contain 1–9, named for the X the diagonals form.
- Is diagonal sudoku harder than classic?
- Slightly — the extra constraints usually make it faster once you remember to scan the diagonals.
- Do both diagonals have the rule?
- Yes, both the top-left-to-bottom-right and top-right-to-bottom-left diagonals.
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