Getting you started with the previously mentioned Tree module:
use Tree ();
my %nodes;
while (<>) {
my ($child, $parent) = split /:/;
my $parent_node = $nodes{$parent} ||= Tree->new($parent);
my $child_node = $nodes{$child} ||= Tree->new($child);
$parent_node->add_child($child_node);
}
my @roots = grep { $_->is_root } values %nodes;
die("Invalid data: No roots\n")
unless @roots;
foreach (@roots) {
...
}
If you are only expecting one root, replace the bottom loop with:
die("Invalid data: Multiple roots\n")
if @roots > 1;
my $root = $roots[0];
...
I didn't check for circular dependancies.
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