$"x=$%="@ARGV";$~=$;='(  +)';while($%>>$:++){if($"=~/$~$/^$"=~/$;$/){$
|=$?=$:>2||die"prime\n";eval"print length(\$$?)".($:>++$?&&"/length(\$
$?).'*'")while$:>$?;die$/}$;=$~;$~=~s~.*~^($&\\1+)~;$~=~s;\d+;1+$&;eg}

[download]

The best thing I can say about this code is that it works. It will take a number via argv give you the prime factorization of that number... eventually. It's not very efficient. At all. I had a lot of fun writing it, but it's really bad at what it does. To give you an idea of how erratic it is, here are some benchmarks:

Kevin@muzyx /cygdrive/c/users/kevin
$ time perl lol.pl 10000
2*2*2*2*5*5*5*5

real    0m4.001s
user    0m3.977s
sys     0m0.015s

Kevin@muzyx /cygdrive/c/users/kevin
$ time perl lol.pl 32767
7*31*151

real    0m6.891s
user    0m6.832s
sys     0m0.031s

Kevin@muzyx /cygdrive/c/users/kevin
$ time perl lol.pl 32768
2*2*2*2*2*2*2*2*2*2*2*2*2*2*2

real    2m50.119s
user    2m49.588s
sys     0m0.015s

Kevin@muzyx /cygdrive/c/users/kevin
$ time perl lol.pl 32769
3*3*11*331

real    0m13.282s
user    0m13.213s
sys     0m0.015s

Kevin@muzyx /cygdrive/c/users/kevin
$ time perl lol.pl 65535
3*5*17*257

real    1m11.228s
user    1m8.422s
sys     0m0.061s

Kevin@muzyx /cygdrive/c/users/kevin
$ time perl lol.pl 65536
2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2

real    22m20.875s
user    20m55.277s
sys     0m0.920s

Kevin@muzyx /cygdrive/c/users/kevin
$ time perl lol.pl 65537
prime

real    0m0.903s
user    0m0.842s
sys     0m0.031s

Kevin@muzyx /cygdrive/c/users/kevin
$ time perl lol.pl 65538
2*3*3*11*331

real    1m40.633s
user    1m40.183s
sys     0m0.077s

Kevin@muzyx /cygdrive/c/users/kevin
$ time perl lol.pl 100000
2*2*2*2*2*5*5*5*5*5

real    20m59.463s
user    20m53.998s
sys     0m0.202s

Kevin@muzyx /cygdrive/c/users/kevin
$ time perl lol.pl 100003
prime

real    0m2.090s
user    0m2.043s
sys     0m0.046s

Kevin@muzyx /cygdrive/c/users/kevin
$ time perl lol.pl 1000003
prime

real    3m23.670s
user    3m22.411s
sys     0m0.062s

[download]

While it can distinguish primes at a reasonable rate, it takes a really long time to factor composite numbers. Particularly composite numbers made up of several small primes. Powers of 2 are the worst-case scenario.

for$b(-25..25){for$a(-50..29){$x=$a/21;$y=$b/15;print$b?chr:chr^chr
ord(substr'<6C}'.1x29 .'[FDEq2?@E96Cqa6C=q924',$a)-49;$_=30;($y,$x)
=(2*$x*$y+$b/15,$x*$x-$y*$y+$a/21)while$x*$x+$y*$y<9&$_++<95}$_=10}

[download]

Replies are listed 'Best First'.
Re: How not to do prime factorization
by atcroft (Abbot) on Jun 30, 2015 at 16:46 UTC

    Here was my simplistic factoring one-liner, and its results on the first digits from pi (1-11).

    Code: 

    perl -Mstrict -Mwarnings -le 'my $n = shift or die qq{Requires 1 numbe
+r argument.}; my $o = $n; my @f = (); my $i = 2; while ( $n % $i == 0
+ ) { push @f, $i; $n /= $i; } $i++; while ( $n >= $i ) { while ( $n %
+ $i == 0 ) { push @f, $i; $n /= $i; } if ( $n > $i ) { $i += 2; } } p
+rint $o, q{ = }, join q{*}, @f;'

    [download]

    Output:

    Read more... (2 kB)

    Enjoy.

[reply]
[d/l]
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Re: How not to do prime factorization
by QM (Parson) on Jun 30, 2015 at 15:49 UTC
    Geez! A really naive regex solution is very quick, but limited to <= 65535: 
    #!/usr/bin/env perl
use strict;
use warnings;

my $candidate = shift;
my $candidate_string= ('x' x $candidate);

while (1) {
    if (my ($factor,$rest) = $candidate_string=~ m/^(..+?)(\1+)$/) {
        print length($factor), "*";
        $candidate /= length($factor);
        $candidate_string= ('x' x $candidate);
    } else {
        print $candidate;
        last;
    }
}

print "\n";

exit;

    [download]

    -QM
    --
    Quantum Mechanics: The dreams stuff is made of

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