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I first have to say that I really enjoyed this problem. It took me a little while to come up with a working algorithm, unfortunately it wasn't at elegant as yours. I thought I would play with your version to see if I could improve upon it a bit. The only thing I could do was add the use of references which reduces the memcopy time on larger lists. Below is a script that benchmarked the old 'non_ref' vs. the new 'ref'. Not necessarily staggering, but an improvement. I compacted the for loop for flipping it around and putting the for statement at the end of the conditional line.
#!/usr/bin/perl use Benchmark; my $count = 100; my $end = 30; sub ref { my $a = [1]; for(1..$end){ # print "@$a\n"; my @na; ($na[-1] == $_ ? $na[-2]++ : push @na, (1, $_)) for @$a; $a = \@na; } } sub no_ref { my @a = (1); my @na; for (1..$end){ # print "@a\n"; @na = (); ($na[-1] == $_ ? $na[-2]++ : push @na, (1, $_)) for @a; @a = @na; } } timethese($count, { 'no_ref' => \&no_ref , 'ref' => \&ref} ); + +
Benchmark: timing 100 iterations of no_ref, ref...
    no_ref: 11 wallclock secs (11.12 usr +  0.04 sys = 11.16 CPU)
       ref:  9 wallclock secs ( 8.34 usr +  0.06 sys =  8.40 CPU)  

In reply to RE: RE: Generating a Pattern by eak
in thread Generating a Pattern by japhy

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