use Data::Dumper;
my $delim   = 'A -3 C -4 B';
my $array   =  
     ['A -4 A','A -1 C','C -4 D','D -4 B','B -3 C','C -2 B','B -1 E'];

get_delim_region($delim,$array);

sub get_delim_region{

    my ($delim,$array)	= @_;
    my $delim_reg = decomp_str($delim);

    # I'm really stuck from here.....

    my @instances;
   
    OUT:
    foreach  my $delim_rg ( @{$delim_reg}  ){
        my @delimreg;
        my $st1 = (split(" ",$delim_rg))[0];
        my $st2 = (split(" ",$delim_rg))[2];
 
        IN:
        foreach  my $i ( 0 ..  @{$array}-1  ){
            my $tr1 = (split(" ",$array->[$i]))[0];
            my $tr2 = (split(" ",$array->[$i]))[2];

            if($st1 eq $tr1){
                push @delimreg,$array->[$i];
            }
            elsif($st2 eq $tr2){
                push @delimreg,$array->[$i];
                next OUT; 
            }
            push @instances, [ @delimreg ]; 
        }     
     }
      print Dumper \@instances;
      return ;
}	

sub decomp_str{

    # This subroutine decompose a string into sub-regions i.e
    # from:  $delim       = 'A -3 C -4 B';
    # into:  $delim_reg   = ['A -3 C','C -4 B'];

    # Credit Roy Johnson - fastest

    [$_[0] =~ /(?=([a-z]\s*(?:\S+\s*){2}))\S+\s*/gi ]
}