Suppose we have hyper sudoku.
In the dark gray areas, we can have 1-9 only once. Therefore, when solving a sudoku graph, I need to figure out what region to look over, to see if any repeats occur.
What is the mathematical expression I can use to find this "region"?
For example, given that the top left $1$ is $(0,0)$, the circled $9$ is at $(2,2)$, where row is $2$, col is $2$.
This region spans from $(1,1)$ to $(3,3)$.
Similarly, the $1$ circled in the bottom left located at $(6,5)$ is spanning region $(5,5)$ to $(7,7)$.
This is clear from visual, but for a mathematical expression, what can be used to figure out the region?
I assume mod must be used, but cannot think of the expression that would work for all cases.
For a problem this small it is probably easier to just list the four regions. The bottom left would be row in $[5,7]$ column in $[1,3]$
If you want a fancy looking math formula or have a larger grid it would be $[4k+1,4k+3]$ in each direction.