It appears to me that each of your triple (X # Y) is a piece of a route with X being the starting point and Y being the end point.

What you seem to have in $array is a long route and a shorter one in $delim.

No you seem to want to find regions in $array that give you the same stop on the long route, you got on the short.

So here is my idea:

1. Make two HoA where you store for each starting and each end point a list of indeces in your $array where to find them
   example data structure:

   %start = (
     A => [ 0, 1, ],
     B => [ 4, 6, ],
     C => [ 2, 5, ],
     D => [ 3, ],
   }
   %end = {
     A => [ 0, ],
     B => [ 3, 5, ],
     C => [ 1, 4, ],
     D => [ 2, ],
     E => [ 6, ],
   );
   [download]

2. With this information you can easily find, for each starting point, where it is located.
3. You will also find easily where each end point can be found.
4. A valid route from A to C are now all those ranges where the value from @{$start{'A'}} is less or equal to a value from @{$end{'C'}}
   This should be:
   A C
   0 1
   0 4
   1 1
   1 4
   
5. Implementation is left as an excercise to you ;-)