in reply to Re: Re: Big Picture
in thread constructing large hashes

Actually, I (fortunately) do not need two for loops. The main loop of my code is this:
$i = 'A'; # the class label for $n (@temp) { next if defined $arrangements{$n}; # already classified it. @n = split /,/, $n; @classmates = ( $n, join(',', reverse @n) ); # n and its mirror @classmates = (@classmates, &M1(@n)); # Maz 1 @classmates = (@classmates, &M2(@n)); # Maz 2 @classmates = (@classmates, &M3(@n)); # Maz 3 &ClassReunion( $i, \@classmates ); $i++; }

M1, M2, and M3 are the three moves (literally, the permutations represent lines in space) which return a new list of permutations. &ClassReunion just does some magic with the label $i.

M1 is easy, it is just the cyclic permutations of the list Ex: M1(12345) -> 51234, 45123, 34512, 23451. sub M1 { map join(',', @_[$_..$#_], @_[0..$_-1]), 1..$#_ }

M2 is the inverse permutation. The permutation 4132 is equivalent to tr/1234/4132/. The inverse would then be tr/4132/1234/.

sub M2 { my %temp; @temp{(1..@_)} = @_; %temp = reverse %temp; return join(',', @temp{(1..@_)}); }

M3 is, unfortunately much harder to explain, and has much longer code. I've posted a working version of the code on my sratchpad. If you /msg me I will post a better explanation of M3 there as well.

Good Day,

If we didn't reinvent the wheel, we wouldn't have rollerblades.

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Re: Re: Re: Re: Big Picture
by petral (Curate) on Oct 03, 2002 at 20:21 UTC
               @classmates = (@classmates, &M1(@n));
    Just a quick check reveals:
    > perl -lwe'use Benchmark "cmpthese";@a=0..8;cmpthese(-8, {push => sub +{push@x,@a[0..2]}, comb => sub{@y=(@y,@a[0..2])}})' Benchmark: running comb, push , each for at least 8 CPU seconds ... comb: 28 wallclock secs (28.33 usr + 0.00 sys = 28.33 CPU) @ 44.7 +9/s (n=1269) push: 8 wallclock secs ( 8.13 usr + 0.25 sys = 8.38 CPU) @ 4172 +8.04/s (n=349681) Rate comb push comb 44.8/s -- -100% push 41728/s 93056% --
    I know your arrays aren't growing linearly like this, so the difference wouldn't be so extreme.