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Re: Permuting with duplicates and no memory

by spx2 (Chaplain)
on Mar 02, 2010 at 03:26 UTC ( #826060=note: print w/ replies, xml ) Need Help??


in reply to Permuting with duplicates and no memory

I feel a bit indebted to write the results of a benchmark I made to find out which of the permutation generators are fast, Algorithm::Permute , tye's implementation , dragonchild's implementation and of course my Steinhaus Johnson Trotter XS implementation:

Rate tye SJT dchld A::P tye 1.27/s -- -22% -46% -81% SJT 1.63/s 28% -- -30% -76% dchld 2.34/s 84% 44% -- -65% A::P 6.67/s 423% 310% 185% --
Here's the code I used to make the benchmark:
use strict; use warnings; use Benchmark qw/cmpthese timethese/; use Algorithm::Permute; use SJT; my $n = 8; # objects to permute my $iter=4; sub nextPermute(\@) { my( $vals )= @_; my $last= $#{$vals}; return "" if $last < 1; # Find last item not in reverse-sorted order: my $i= $last-1; $i-- until $i < 0 || $vals->[$i] lt $vals->[$i+1]; # If complete reverse sort, we are done! return "" if -1 == $i; # Re-sort the reversely-sorted tail of the list: @{$vals}[$i+1..$last]= reverse @{$vals}[$i+1..$last] if $vals->[$i+1] gt $vals->[$last]; # Find next item that will make us "greater": my $j= $i+1; $j++ until $vals->[$i] lt $vals->[$j]; # Swap: @{$vals}[$i,$j]= @{$vals}[$j,$i]; return 1; } sub make_orderings { my $num = shift; my @arr = (1 .. $num); return sub { my $last = $#arr; my $i = $last - 1; $i-- while 0 <= $i && $arr[$i] >= $arr[$i+1]; return if $i == -1; @arr[$i+1..$last] = reverse @arr[$i+1..$last] if $arr[$i+1] > $arr[$last]; my $j=$i+1; $j++ while $arr[$i] >= $arr[$j]; @arr[$i,$j] = @arr[$j,$i]; return @arr; } } cmpthese( $iter, { 'A::P' => sub { use Algorithm::Permute; my $p = new Algorithm::Permute([1..$n], $n); while (my @res = $p->next) { #print join(", ", @res), "\n"; } }, 'SJT' => sub { my $s = SJT->new($n); while($s->next_perm()){ my @p = @{$s->{permutation}}; #$s->print_perm; }; }, 'tye' => sub { my @w= (1..$n); do { } while( nextPermute(@w) ); }, 'dchld' => sub { my $i = make_orderings($n); while(my @a = $i->()){ }; }, } );


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