перестановки

[ocehb]

sub shuffle (@) {
    return ( [ $_[0],$_[1] ],[ $_[1],$_[0] ] ) if (scalar @_ == 2);

    my $b = shift @_;
    my @ret;
    foreach my $r (shuffle (@_)) {
        foreach (0..scalar @$r) {
            my (@rr) = @$r;
            splice @rr,$_,0,$b;
            push @ret,\@rr;
        }
    }
    return @ret;
}

# time perl a.pl 1 2 3 4 5 6 | wc -l
     720
Real: 0.07s User: 0.05s System: 0.01s Percent: 90%% Cmd: perl a.pl 1 2 3 4 5 6
Real: 0.07s User: 0.00s System: 0.00s Percent: 5%% Cmd: wc -l
# time perl a.pl 1 2 3 4 5 6 7 8 9 | wc -l
  362880
Real: 7.43s User: 6.65s System: 0.63s Percent: 98%% Cmd: perl a.pl 1 2 3 4 5 6 7 8 9
Real: 7.42s User: 0.07s System: 0.01s Percent: 1%% Cmd: wc -l
# time perl a.pl 1 2 3 4 5 6 7 8 9 0 | wc -l
Out of memory during request for 1012 bytes, total sbrk() is 536786944 bytes!
       0
Real: 56.49s User: 16.54s System: 4.47s Percent: 37%% Cmd: perl a.pl 1 2 3 4 5 6 7 8 9 0
Real: 56.49s User: 0.00s System: 0.00s Percent: 0%% Cmd: wc -l
#

Comments

Re: хех. умеет :)

[lispnik.livejournal.com]

Нет, не оно :)
А gcc действительно умеет превращать хвостовую рекурсию в цикл, но только если список аргументов достаточно простой...