Does Sudoku Have a Diagonal Rule?
One of the reasons so many people love sudoku is because of the simplicity of its rules:
- Each column has to contain the numbers 1 through 9 exactly once each without repeating
- Each row has to contain the numbers 1 through 9 exactly once each without repeating
- Each 3×3 region has to contain the numbers 1 through 9 exactly once each without repeating
But what about the two 9 cell diagonals found in sudoku grids? Must these two diagonals also contain every number from 1 through 9 exactly once each as well?
In other words:
Does sudoku go diagonal?
The short answer is: no.
In regular sudoku there are no diagonal rules that state the two 9 cell diagonals must contain all the numbers 1 through 9. There is however a variant of sudoku that does add this rule as an additional constraint: diagonal sudoku (also known as X sudoku).
However, unless you are playing this particular variant, or any other variants with a diagonal rule, you do not need to worry about the diagonals. Trying to ensure that the numbers 1 through 9 only appear once in every diagonal is likely to make regular sudoku puzzles unsolvable as well.
Would a diagonal rule make sudoku harder to solve?
It might be to think that the absence of a sudoku diagonal rule would mean that the puzzle becomes easier to solve. After all, it’s natural to think that the fewer constraints the more possibilities there are.
However, sudoku is a game where you must eliminate the possibility of all the digits appearing in a particular cell apart from a single digital.
The additional constraint means that you potentially have more information to work with when trying to figure out which digit goes into one of the cells along either of the long diagonals.
Where you can play diagonal sudoku
If you’re looking to play a game of diagonal sudoku where you have the additional diagonal constraint, you can play it online at the following places:
What about other diagonals in the grid?
In terms of all the other shorter diagonals in the grid, there are few if any variants that require you to pay special attention to them.