Triplets :: S=('b,c|a', 'a,c|d', 'd,e|b'),
Species :: L={a,b,c,d,e}
TreeConstruct(S):
1.] Let L be the set of species in S. Build G(L) the auxillary graph.
2.] Let C1,C2....Cq be the set of connected components in G(L).
3.] If q>1,then
   - For i=1,2.....q, let S(i) be the set of triplets in S labeled by the set of leaves in C(i).
   - Let T(i) = TreeConstruct(S(i))
   - Let T be a tree formed by connecting all T(i) with the same parent node. Return T.
4.]If q=1 & C1 contains exactly one leaf,return the leaf ,else return fail.
##</code><code>##

use strict;  
use warnings;   
use Graph;  
@ARGV =  ('b,c|a', 'a,c|d', 'd,e|b') unless @ARGV;   
  
my %HoA;  
foreach ( @ARGV ) {  
    m/^([a-z])[,]([a-z])[|]([a-z])$/ ;  
    push @{$HoA{$1}}, $2;  
}  
print "\n===========\@HoA=====\n";  
print "from->to\n";  
while (my ($key, $values) = each %HoA) {  
    print $key, "=>   [", join(',', @$values), "]\n";  
}  


my $g = Graph->new( undirected => 1 );

for my $src ( keys %HoA ) {
    for my $tgt ( @{ $HoA{$src} } ) {
        $g->add_edge($src, $tgt);
    }
}

my @subgraphs = $g->connected_components;
my @allgraphs;

for my $subgraph ( @subgraphs ) {
    push @allgraphs, {};
    for my $node ( @$subgraph ) {
        if ( exists $HoA{ $node } ) {
            $allgraphs[-1]{$node} = [ @{ $HoA{$node} } ];
        }
    }
}
print "----connected components------------";
use YAML; print Dump \@allgraphs;
-------------OUTPUT----------------
===========@HoA=====
from->to
a=>   [c]
b=>   [c]
d=>   [e]
----connected components---------------
- a:
    - c
  b:
    - c
- d:
    - e