Borrowing from
Laurent_R's answer, you might want to consider using
Graph::Undirected to get the connections. I also borrowed this graph example from somewhere, probably from here at Perl Monks but can't find the original in a search.
#!/usr/bin/perl
use strict;
use warnings;
use Graph;
my $g = Graph::Undirected->new;
while (<DATA>) {
chomp;
my ($x, $y) = split /;/;
$y = $x if $y eq ''; # will pass $y == 0 if that's the case
$g->add_edge($x, $y);
}
my %pred;
for my $aref ($g->connected_components) {
my @items = sort {$a <=> $b} @$aref;
my $first = $items[0];
for my $element (@items) {
$pred{$element} = $first;
}
}
print "$_ => $pred{$_}\n" for sort {$a <=> $b} keys %pred;
__DATA__
567;456
456;345
345;234
234;123
339;228
228;117
131;
435;324
324;213
372;
Prints:
117 => 117
123 => 123
131 => 131
213 => 213
228 => 117
234 => 123
324 => 213
339 => 117
345 => 123
372 => 372
435 => 213
456 => 123
567 => 123
Update: Changed
$g->add_edge($x, $y || $x); to
$g->add_edge($x, $y); and added
$y = $x if $y eq ''; so to allow $y to be a possible zero.
