#!/usr/bin/perl
use strict;
use warnings;

my %lookup_ids_by_line;
my %lookup_lines_by_id;

chomp (my @lines = <DATA>);

foreach my $line (@lines) {

    my ($id1, $id2) = $line =~ m/\.(\S+)/g;

    push(@{$lookup_ids_by_line{$line}}, $id1, $id2);
    push(@{$lookup_lines_by_id{$id1}}, $line);
    push(@{$lookup_lines_by_id{$id2}}, $line);
}

my $cluster_number = 0;

foreach my $line (@lines) {
    next unless(exists($lookup_ids_by_line{$line}));

    $cluster_number++;

    my @lines_in_cluster = ($line);
    my @ids_to_check = @{$lookup_ids_by_line{$line}};

    delete($lookup_ids_by_line{$line});

    while(@ids_to_check) {
        my $id = pop(@ids_to_check);
        next unless(exists($lookup_lines_by_id{$id}));

        foreach my $line (@{$lookup_lines_by_id{$id}}) {

            if(exists($lookup_ids_by_line{$line})) {
                push(@lines_in_cluster, $line);
                push(@ids_to_check, @{$lookup_ids_by_line{$line}});

                delete($lookup_ids_by_line{$line});
            }
        }

        delete($lookup_lines_by_id{$id});
    }
    print "cluster number $cluster_number:\n\t" .
        join("\n\t",@lines_in_cluster) . "\n";
}

__DATA__
ID5141.C1665 ID5141.C2448
ID5141.C1253 ID5144.C2039
ID5141.C1596 ID5144.C1956
ID5141.C1906 ID5144.C2149
ID5141.C1221 ID5144.C1956
ID5141.C2149 ID5141.C2386
ID5141.C2039 ID5142.C1221
ID5141.C5887 ID5141.C7685
ID5141.C1005 ID5142.C2808
ID5141.C1046 ID5141.C1596
ID5141.C2386 ID5141.C4990
ID5141.C7685 ID5141.C4888