Code Golf: Prime Factors of a Number [closed]

Answer 1

Best Perl answer yet - 70 characters, and no extra modules (unless you count special features of 5.10):

perl -nE'sub f{($a)=@_;$a%$_||return$_,f($a/$_)for 2..$a}$,=x;say f$_'

Doesn't work for 1 or 0, but works fine for everything else. If you don't like using say, or are using an earlier version of Perl, here's an 81 character version:

perl -ne'sub f{($a)=@_;$a%$_||return$_,f($a/$_)for 2..$a;}$,=x;$/="\n";print f$_'

Answer 2

Wow, you guys aren't very good at optimizing. I can do it in Perl in 63 characters, or 79 if you insist on including a #!/usr/bin/perl at the top:

use Math::Big::Factors;
@f=factor_wheel($ARGV[0],1);
print @f;

(Don't look at me that way. Committed programmers are lazy programmers.)

Answer 3

Perl, 70 char

$y=<>;for($i=2;$i<=$y;){next if$y%$i++;$y/=--$i;push@x,$i}print@{$,=x}

Answer 4

GNU bc, 47 chars, including collecting input (need the GNU extensions for print, else and read):

x=read();for(i=2;x>1;)if(x%i){i+=1}else{x/=i;i}

If you really want the x characters in the output, it's 64 chars:

x=read();for(i=2;x>1;)if(x%i){i+=1}else{x/=i;print i;if(x>1)"x"}

Also, note that using bc allows this to process numbers of arbitrary length.

Answer 5

11 characters in APL

Excluding function header and newlines

factors←{2÷/∪⌽∧\⍵∨⍳⍵}

Answer 6

C#, 69

x is input number

int i=2;while(x>1)if(x%i++==0){x/=--i;Console.Write(i+(x>1?"x":""));};

With includes:

using system;
namespace nameSP
{
   class Program
   {
     static void Main(string[] args)
     { 
        int i=2;while(x>1)if(x%i++==0){x/=--i;Console.Write(i+(x>1?"x":""));};
     }
   }
}