Question

Say I have an index 12 (12th element) going from left to right, top to bottom.

I have an array[4][4].

What would be the fastest way to compute the index [3][2] given the 1D index 12? (1D index starts at 1).

Thanks

Answer 1

Don’t know if this is fastest, but it’s definitely simple:

Assuming array[x][y]

ix = floor(index / y)
iy = index % y

Example:

01
23
45

x = 3
y = 2

index = 3
ix = floor(3 / 2) = 1
iy = 3 % 2 = 1    

index = 5
ix = floor(5 / 2) = 2
iy = 5 % 2 = 1