Perl, how to make this scripter smaller, faster, better, stronger? [closed] - performance

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I'm a newbie in perl, how I can make this better and faster?
(SPOJ task)
until($i>99){
$a=<>;
if($a%5==0){
if($a%3==0){
print"SPOKOKOKO\n";
}else{
print"SPOKO\n";
}
}elsif($a%3==0){
print"KOKO\n";
}else{
print"$a";
}
$i++;
}

Answer 1

Something which is divisible by 5 and 3 is divisible by 15, so your logic is more straight forward as...
Divisible by 15
Divisible by 5
Divisible by 3
Not divisible by 5 nor 3
I'd also take advantage of say.
I'd also replace the awkward until with a for and not bother with $i.
Avoid using $a and $b because these are special variables used by sort.
Turn on strict and warnings.
Strip the newline off $a. Technically not necessary if you're going to use it as a number, but if you don't printing it will have an extra newline.
A non-number % anything is 0. Unless we validate the input, if you input nothing or "bananas" you'll get SPOKOKOKO. We can check if the input looks like something Perl considers a number with Scalar::Util::looks_like_number. If it isn't a number, throw an exception; it isn't the function's job to figure out what to do with a non-number. Perl doesn't really have exceptions, but we can get close with a die and eval.
And put the logic inside a subroutine. This separates the details of the input and output from the logic. The logic can now be named, documented, tested, and reused. This also avoids the redundant say.
use strict;
use warnings;
use Scalar::Util qw(looks_like_number);
use v5.10;
sub whatever_this_is_doing {
my $num = shift;
# Validate input early to keep the rest of the logic simple.
if( !looks_like_number($num) ) {
die "'$num' is not a number";
}
if($num % 15 == 0) {
"SPOKOKOKO";
}
elsif($num % 5 == 0) {
"SPOKO";
}
elsif($num % 3 == 0) {
"KOKO";
}
else {
$num; # Note there's no need to quote a single variable.
}
}
for(1..99) {
my $num = <>;
chomp($num);
eval {
say whatever_this_is_doing($num);
} or say "'$num' is not a number.";
}
I'm sure there's some very clever math thing one can do to reduce the number of calls to %, but % is extremely unlikely to be a bottleneck, especially in Perl, so I'd leave it there.

Answer 2

100 rows? That will be so fast that I don't understand why you are asking for optimization. Nevertheless...
The biggest two costs are reading 100 rows and writing 100 rows.
Then come the ifs and modulo checks -- each of these is insignificant.
One thing to consider is to turn it inside out. I'm suggesting 1 print with a messy expression inside the loop
print ( ($a%5 == 0) ?
( ($a%3 == 0) ? "SPOKOKOKO\n" : "SPOKO\n" ) :
( ($a%3 == 0) ? "KOKO\n" : $a );
A lot fewer lines (3 vs 10); probably easier to read (especially if columns are aligned); perhaps faster.
Easier to digest. (I had not noticed that the %3 was s the same.) Oh, and now it is obvious that \n is missing from the last case; maybe a bug?
Perhaps some of the parentheses can be removed, but I don't trust Perl to 'do the right thing with nested uses of ?:.