Find prime factors

Question

A whole program to find the prime factors of a given number. The number will be given on standard input.

Answer 1

Bash Shell

6 Chars

factor

If rot13 can be allowed, i don't see why this one is an issue...I'm sorry but this is very trivial.

Answer 2

J - 2 characters

q:

Example:

   q: 31415
5 61 103

Answer 3

dc, 48 chars

[ldp0<x]sp?2sd[[dsrld~0=p]dsxxcld1+sdlrd1<y]dsyx

Answer 4

Ruby - 50 49 47 44 42 chars

2.upto(n=gets.to_i){|i|n/=p i while n%i<1}

Answer 5

Python: 58

n=input()
for i in range(2,n+1):
 while n%i<1:print i;n/=i

Answer 6

Perl, 42 chars

map{$n/=$_,print$_,$/until$n%$_}2..($n=<>)

Answer 7

Windows PowerShell, 46

Naïve solution.

2..($x=+"$input")|%{for(;!($x%$_)){$_;$x/=$_}}

Answer 8

Pure Bash Solution (60 characters)

Based on F.Hauri's solution (thanks to him):

read p;for((i=2;p-1;));do((p%i++||(p/=--i)*0))||echo $i;done

Answer 9

Python (55)

based on marcog

n=input()
i=1
while~-n:
 i+=1
 while n%i<1:print i;n/=i

Answer 10

C (68)

Not the shortest, but I was curious to see how a C solution could compare.

d=2;main(n){scanf("%d",&n);for(;n>1;)n%d?++d:printf("%d\n",d,n/=d);}

Answer 11

100% Pure bash: 72 chars

read p;for((i=1;p>i++;));do while((p%i<1));do echo $i;((p/=i));done;done

or

read p;i=1;while((p>i++));do while((p%i<1));do o+=$i\ ;((p/=i));done;done ;echo $o

This seem longer, but in replacing for by while, I could make an overall loop and using alias to reduce then code:

alias D=done W=while
prime() { W read p;do i=1 o=;W((p>i++));do W((p%i<1));do o+=$i\ ;((p/=i));D;D;echo $o;D;}
unalias D W

This way, my (written) code whith the loop is 77 char length.

Anyway, the function is memorized with full command names:

declare -f prime
prime () 
{ 
    while read p; do
        i=1 o=;
        while ((p>i++)); do
            while ((p%i<1)); do
                o+=$i\ ;
                ((p/=i));
            done;
        done;
        echo $o;
    done
}

Answer 12

Mathematica, 26 chars

#&@@@FactorInteger@Input[]

Answer 13

R, 72 characters

Just for the kicks, an attempt without using any preexisting function to prime-factorize:

n=scan(n=1);m=1:n;M=m[!n%%m&!m%in%c(1,n)];M[rowSums(!outer(M,M,`%%`))<2]

Ungolfed with explanations:

n <- scan(n=1) #Take one number from stdin
m <- 1:n
#Of which of the integers from 1 to n is n a multiple (excluding 1 and himself):
M <- m[!n%%m & !m%in%c(1,n)] 
#Trim that list by excluding integers that are multiples of others in the list:
M[rowSums(!outer(M,M,`%%`))<2]

NB: Instead of checking if n%%m==0, use the fact the 0 coerce as FALSE when using !.

Answer 14

Javascript (54)

n=prompt()*1;for(i=2;n>1;n/=n%i?(++i,1):(alert(i),i));

Answer 15

perl5.10: 36 chars

map{$p/=$_,say until$p%$_}2..($p=<>)

Answer 16

Haskell 74 chars

s n=f((==0).mod n)[2..n]
main=readLn>>=print.f((==1).length.s).s
f=filter

Example

12 -> [2,3]
128 -> [2]
60 -> [2,3,5]

Answer 17

Octave, 17 chars

factor(input(''))

Answer 18

Scala 111:

def f(i:Int,c:Int=2):List[Int]=if(i==c)List(i)else
if(i%c==0)c::f(i/c,c)else f(i,c+1)
f(readInt).mkString(" ")