Re^3: Can you write a faster code to perform this task?

[trizen]

What about something like this?

use 5.014;

say 'iiiiiiiiMMMMMMMMMMMooooooooooooMMMMMMMMMMiiiiiMMMMMMMMoooo' 
      =~ tr/M/~/sr=~tr/~//;   # => prints: 3

Update: just to be sure, it would be safer to replace 'M' with something much exotic, like '\0', which should be OK, assuming that you're reading text files. (tr/M/\0/sr =~ tr/\0//)

[Lotus1]

I tried it with replacing 'M' with 'M' and it worked. No need to worry about exotic characters.

use 5.014;

say 'iiiiiiiiMMMMMMMMMMMooooooooooooMMMMMMMMMMiiiiiMMMMMMMMoooo' 
      =~ tr/M/M/sr=~tr/M//;   # => prints: 3

[BrowserUk]

No need for a new perl and the /r option either. This works fine:

#! perl -slw
use strict;
use Time::HiRes qw[ time ];

my $start = time;
my $count=0;
while( <DATA> ) {
#    $count += ()= m{M+}g;
    tr/M/M/s;
    $count += tr/M/M/;
}
print $count."\n";

printf "Took %9f secs\n", time() - $start;

[LanX]

Well TIMTOWTDI with two chained tr is not necessarily fast. :)

But who knows, try to benchmark... :)

[Your Mother]

tr is MUCH faster than s though. I tried to work this out but didn’t hit on trizen’s cleverness. So…

# (v5.18.2) built for darwin-2level
    'tr' => sub {
        $str =~ tr/M/~/sr=~tr/~//;
    },
-- 
count      3
regex      3
regex2     3
split      3
tr         3

            Rate regex2  split  regex  count     tr
regex2  169354/s     --   -62%   -65%   -75%   -94%
split   446500/s   164%     --    -7%   -34%   -85%
regex   481882/s   185%     8%     --   -29%   -84%
count   674634/s   298%    51%    40%     --   -78%
tr     3044813/s  1698%   582%   532%   351%     --

Update: as trizen noted in his code, the /r flag to tr came in at 5.14. It won’t work on older Perls (update: <- stupid apostrophe begone).

[LanX]

> I tried to work this out but didn’t hit on trizen’s cleverness.

me too / neither =)

(tried /s but the returned count wasn't for groups)

> the /r flag to tr came in at 5.14. It won’t work on older Perls

If it's that fast using $str twice shouldn't be a big problem.

Should be mentioned that tr is destructive, i.e. a safety copy of the string may be needed too.