I noticed that your fast permutation algorithm passes an arrayref, but then copies the values out. There's no particular savings there compared to passing the array. That and a few other micro-optimizations squeezed
210+% more speed out (if you don't print — the savings are probably less significant with printing turned on.) Code (update: fixed, reducing savings, as expected) follows.
{
my $level = 0;
sub permute_new {
local @_ = @_;
my $index = $level;
my $printing = $level == $#_;
if ($printing) {
do {
#print "@_\n";
@_[$index-1, $index] = @_[$index, $index-1]
if $index != 0;
} while $index-- > 0;
}
else {
do {
++$level;
&permute_new;
--$level;
@_[$index-1, $index] = @_[$index, $index-1]
if $index != 0;
} while $index-- > 0;
}
}
}
sub permute_orig {
my ($aref, $level) = (@_, 0);
my ($index, $copy, $printing) = ($level, [@$aref], $level+1 == @$a
+ref);
do {
if ($printing) {
#print "@$copy\n";
} else {
permute_orig($copy, 1+$level);
}
@$copy[$index-1, $index] = @$copy[$index, $index-1]
if $index != 0;
} while $index-- > 0;
}
my $to = shift;
use Time::HiRes qw( gettimeofday tv_interval );
my @start_time = gettimeofday();
permute_orig([1..$to]);
print "\n";
my @end_time = gettimeofday();
print tv_interval ( \@start_time, \@end_time )," elapsed seconds for o
+riginal.\n\n";
@start_time = gettimeofday();
permute_new(1..$to);
@end_time = gettimeofday();
print tv_interval ( \@start_time, \@end_time )," elapsed seconds for n
+ew.\n\n";
Caution: Contents may have been coded under pressure.