sub _findPaths3 {
    return $_[0]->( @{ $_[4] }, $_[3] ) if $_[2] eq $_[3];
    my %seen; $seen{ $_ } = 1 for @{ $_[4] }, $_[2];
    for ( grep !$seen{ $_ }, @{ $_[1]->{ $_[2] } } ) {
        _findPaths3( $_[0], $_[1], $_, $_[3], [ @{ $_[4] }, $_[2] ] ),
    }
}

sub findPaths3(&@) { _findPaths3( @_, [] ); }