#!/usr/bin/perl
use constant LAST => -1;
use constant PATH => 0;
use constant SEEN => 1;
use strict;
use warnings;

my %graph = (
    F => [qw/B C E/],
    A => [qw/B C/],
    D => [qw/B/],
    C => [qw/A E F/],
    E => [qw/C F/],
    B => [qw/A E F/]
);

my $routes = find_paths('B', 'E', \%graph);
print "@$_\n" for @$routes;

sub find_paths {
    my ($beg, $end, $graph) = @_;
    my @solution;
    my @work;
    for (@{$graph->{$beg}}) {
        push @solution, [$beg, $end] if $_ eq $end;
        push @work, [[$beg, $_], {$beg => undef, $_ => undef}];
    }
    while (@work) {
        my $item = pop @work;
        my ($path, $seen) = @{$item}[PATH, SEEN];
        for my $node (@{$graph->{$path->[LAST]}}) {
            next if exists $seen->{$node};
            my @new_path = (@$path, $node);
            if ($node eq $end) {
                push @solution, \@new_path;
                next;
            }
            my %new_seen = (%$seen, $node => undef);
            push @work, [\@new_path, \%new_seen];
        }
    }
    return \@solution;
}