Pfthb

I have a task:

we have a cube storing 0 or 1. say, elements of the cube are cells.
the size of the cube is given: in direction of i it's Nx, of j it's Ny,
of k it's Nz. we need to fit the cube into a 1D array of the size of Nx * Ny * Nz.

the data is stored in the next order: first we change i, then j, then k.
we need to built an example of such cube, for instance, we can take size of a cube of 100kk, 400*250*1000

we need to find connected 3D regions of the cube (two cells are connected if they have 1 common side and both store 1, and connected region is a set of connected cells), i.e.
we need to find a number of regions and cells that each of them are storing. And speed of computing is important. It should take few seconds to do this task.

The first thing that I did was creating a 1D array of the size of 400*250*1000 storing cube's cells of 0 or 1 (see attached code in c#). Is it correct? The main question is how am I supposed to find regions of cells?

 int Nx = 400;
 int Ny = 250;
 int Nz = 1000;
 int array = new int[Nx*Ny*Nz];
 Random rnd = new Random();
 for (int i = 0; i < Nx; i++) 
 for (int j = 0; j < Ny; j++) 
 for (int k = 0; k < Nz; k++) 
 array[Ny * Nz * i + Nz * j + k] = rnd.Next(2);
 
 
 

I was thinking of using ArrayList both for regions and cells. But how to find cells of a region? Then how to store them?

 ArrayList<Integer> cells = new ArrayList<Integer>(); 
 ArrayList<ArrayList<Integer>> realms = new ArrayList<ArrayList<Integer>>();