順列列挙

next_permutation.pl

sub next_permutation {    my $ary = shift;    return unless ref($ary) eq 'ARRAY';    my $last = $#$ary or return;    my $i = $last;    while ($ary->[$i-1] > $ary->[$i]) {        return unless $i-- > 1;    }    my $j = $last;    while ($ary->[$i-1] > $ary->[$j]) {        $j--;    }    @$ary[$i-1, $j] = @$ary[$j, $i-1];    @$ary[$i..$last] = reverse @$ary[$i..$last];    return 1;}