#!/usr/bin/perl
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, $graph) = @_;
    my (@work, @solution);
    for (@{$graph->{$beg}}) {
        if ($_ eq $end) {
            push @solution, "$beg->$end";
            next;
        }
        my $seen = '';
        vec($seen, node_to_int($_), 1) = 1;
        vec($seen, node_to_int($beg), 1) = 1;
        push @work, ["$beg->$_", $_, $seen];
    }
    while (@work) {
        my $item = pop @work;
        my ($path, $curr, $seen) = @$item;
        for my $node (@{$graph->{$curr}}) {
            my $bit = node_to_int($node);
            next if vec($seen, $bit, 1);
            if ($node eq $end) {
                push @solution, "$path->$end";
                next;
            }
            my $new_seen = $seen;
            vec($new_seen, $bit, 1) = 1;
            push @work, ["$path->$node", $node, $new_seen];
        }
    }
    return \@solution;
}

sub node_to_int {
    my ($node) = @_;
    return ord($node) - 65;
}