comment on

I tried PDL, but it was also very slow (about 49 minutes):

use strict;
use PDL::LiteF;
use PDL::Primitive;
use PDL::Reduce;
use PDL::Types;
use integer;

my ($ans, $total, $total2, $sum, $num, $ones, $zeros);
my $shifts  = long (
               0,
               1,
               1 << 1,
               1 << 2,
               1 << 3,
               1 << 4,
               1 << 5,
               1 << 6,
               1 << 7,
               1 << 8,
               1 << 9,
               1 << 10,
               1 << 11,
               1 << 12,
               1 << 13,
               1 << 14,
               1 << 15,
               1 << 16,
               1 << 17,
               1 << 18,
               1 << 19,
               1 << 20,
               1 << 21,
               1 << 22,
               1 << 23
               );
$ans = 0;
for my $num (0 .. 16777216) {
  $sum = sum(which($shifts & $num));
  $total = 2*$sum - 300;
  $ans++ if $total == 0;
}

print "$ans\n";
[download]

I did much better with Inline::C (about 4 seconds after the first time):

use Inline C;

print "answer is ", bitlevels(), "\n";

__END__
__C__

/* begin c++ code */
/* #include<iostream> */
/* using namespace std; */

int bitlevels()
{
  unsigned int ans=0;
  int num, total, i;
  unsigned int shift;

  for(num=0;num<16777216;++num)
  {
    total=0;  
    shift=1;
    for(i=1;i<=24;++i)
    {
      if(num & shift)
      {
        total+=i;
      }
      else
      {
        total-=i;
      }
      shift<<=1;            
    }
    if(total==0) ++ans;
  }

  return ans;
}
/* end c++ code */
[download]

In reply to Re: Believably slow.. by tall_man
in thread Unbelievably slow.. by kiat

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