use strict;

my %graph = (
    FOO   => [qw/BAR BLAH ASDF/],
    BAR   => [qw/LA/],
    BLAH  => [qw/XYZ/],
    ASDF  => [qw/OOOOO/],
    LA    => [],
    XYZ   => [qw/LA/],
    OOOOO => []
);

my %reversegraph;
for my $x (keys %graph) {
  for my $y (@{ $graph{$x} }) {
    push @{$reversegraph{$y}}, $x;
  } 
}

{
  my %seen;
  my %onstack;
  my @list;

  sub how_to_uninstall {
      my $target = shift;
      (@list, %seen, %onstack) = ();

      _traverse(\%reversegraph, $target);
      my @dependedontarget = @list;

      (@list, %seen, %onstack) = ();
      for my $v (@dependedontarget) {
          _traverse(\%graph, $v) unless $seen{$v};
      }

      return @list;
  } 

  sub _traverse {
      my ($G,$x) = @_;
      $seen{$x} = $onstack{$x} = 1;
      for my $y (@{$G->{$x}}) {
          die "cyclic!" if $onstack{$y};    # back edge
          _traverse($G,$y) unless $seen{$y};
      }
      push @list, $x;
      $onstack{$x} = 0;
  }
}
my @order = how_to_uninstall('BLAH');
print "@order\n";

__OUTPUT__
LA BAR XYZ BLAH OOOOO ASDF FOO
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