[Algorithm for grouping items]

Hi everyone, i have some troubles to solve this "grouping" problem.

 

I have 2D (nxn) array and i want to group all related item to groups.

 

Items are considered to be related in 2 cases: when they have the same edge or top.

$table = array(
 array( 0, 0, 0, 0, 0, 0),
 array( 0, 0, 1, 2, 0, 0),
 array( 0, 0, 0, 0, 0, 0),
 array( 0, 3, 0, 4, 0, 0),
 array( 0, 0, 5, 0, 0, 0),
 array( 0, 0, 0, 6, 0, 7)
);

And this is result which i want to achieve :

$groups= array(
 array( 1, 2),
 array( 3, 4, 5, 6),
 array( 7 ),
);

I will be grateful for any help. THX