(´∀｀) Prime numbers (,,ﾟДﾟ)

|code]isPrime x = (filter (0 ==) (map (mod x) [2..x-1])) == [][/code]

lol

isPrime x = null $ filter (0 ==) $ map (mod x) [2..x-1]

Next up: pointless primality test.

>>3
GOA> :pl \ x -> null $ filter (0 ==) $ map (mod x) [2..x-1]
 null . filter (0 ==) . liftM2 map mod (enumFromTo 2 . subtract 1)

FAPFAPFAP

Prelude Data.List> nubBy (((==0).).flip mod) [2..]
[2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71Interrupted.

isPrime x = divs x 2 where divs x y = if x == y then True else if mod x y == 0 then False else divs x (y + 1)

>>6
That's horrible. It's not a one-liner just because you've removed the newlines.

sub is_prime{$_='x'x pop;/../^/^(..+)\1+$/}

or, if you want something a little faster:
sub is_prime{my$n=pop;map{$n*=$n%$_>0}2..$n**.5;$n>1}

>>8
Is that Battletoads?

>>9
Indeed it is.

>>7
Yes, it is.

   printNPrimes=.p:@i.
   printNPrimes 5
2 3 5 7 11

>>12
Multi-character function names?  In *MY* J?  The sure sign of a novice programmer.

sub factor{my@f,$n=pop;map{$n/=$_,push@f,$_ until$n%$_}2..$n/2;@f}
sub is_prime{!factor pop}

function isPrime($x) {
  for($i=2;$i++<$x;) if(!($x%$i)) return false;
  return true;
}

Whitespace version

nubBy (((==0).).flip mod) [2..]

is an infinite list of all prime numbers. Good luck doing that in your faggot language.

>>16
Fuck

.

>>17
good luck doing what >>14 does in your faggot language

>>17
its pretty easy to write in any language actually

>>19
What does >>14 do?  I can't make anything at all out of it except that it defined two subroutines.

>>21
factor returns a list of prime factors of a number. if the number is prime, it returns an empty list.
is_prime is pretty obvious.

>>15
Very inefficient way to do it in most cases.

#include <math.h>

const size_t NumPrimes = 1000000;

int main(void)
{
    size_t i, j;
    __int64 cur, number;
    __int64 *primes = (__int64 *) 0;

    if (primes = new __int64[NumPrimes]) {
        for (i = 0; i < NumPrimes; i++) {
            primes[i] = 0;
        }

        for (primes[i = 0] = 2, number = 3; i < NumPrimes-1; number++) {
            __int64 max = (__int64) (ceil(sqrt((long double) number)));

            for (j = 0; cur = primes[j]; j++) {
                if (number % cur == 0) {
                    break;
                } else if (cur >= max) {
                    primes[++i] = number;
                    break;
                } else {
                    continue;
                }
            }
        }
       
        delete[] primes;
        primes = (__int64 *) 0;
    }

    return 0;
}

There you have many primes. You can increase NumPrimes to any number you like, but you 'might' need more RAM. :)

>>23
so how do you use that to check if 18446744073709551617 is prime?

>>24
Divide by zero, lol

>>23
Well, you would need a lot of memory to build a list that long, but once you have n primes, finding the next prime is of the order n log(n). The person above advocating the exponential algorithm clearly hasn't got a clue about programming.

>>23
Well, you would need a lot of memory to build a list that long, but once you have n primes, finding the next prime is of the order n log(n). The person above advocating the exponential algorithm clearly hasn't got a clue about programming.

>>24 not >>23 above

>>1 >>3 >>4
You don't need to go 2..x-1, you only need to go 2..sqrt(x)

So I did some benchmarking and came to the conclusion that

List.nubBy (\ a b -> 0 == mod b a) [2..]

is about twice as fast as

List.nubBy (((0 ==).).flip mod) [2..]

Why?

use Quantum::Superpositions;
sub is_prime{$n=shift;$s=any(2..$n-1);return !eigenstates($s*$s=$n);}

p:i. 1000

#!/usr/bin/perl -l

use Quantum::Superpositions;

my $n=any 2..shift;
print join',',eigenstates($n!=all(eigenstates($n==$n*$n)));

>31
use Quantum::Superpositions;
sub is_prime{$n=shift;$s=all(2..$n);$s*$s!=$n}

isPrime = lambda n: n > 1 and n not in set(x*y for x in range(2, n) for y in range(2, n))

>>35
Lol, forced indentation of code.

>>7
`where` is not really considered to make a new line and if-then-else is like a function. If you are going to say someone just removed the new-lines then that line has to have a semi-colon in there somewhere.

>>37
I meant that in the pull-your-head-out-of-you-ass-and-realize-no-sane-person-really-writes-Haskell-like-that-because-it-would-be-completely-unreadable kind of way.

I really do wonder who trolled who this time, though.

>>35
def isprime(n): return n > 1 and not any(n % d == 0 for d in xrange(2, n//2+1))

if-then-else is like a function
This seems like a good time to bring up one of my pet peeves about Haskell. Why _isn't_ if a function? Observe:
if :: Bool -> a -> a -> a
if True then _ = then
if False _ else = else
No ugly keywords fagging my shit up, and unlike if functions in other languages you don't have to worry about both then and else both being evaluated when they could potentially be computationally expensive - thanks to Haskell's laziness you're guaranteed only one will be.

>>40
Oh, I just realized it really isn't a function. I'd like to know the reason, too.

>>40
I think it's because if-then-else looks nice than any real reason. Reasonable name for your function there could be ifte.

>>42
But is there a need for `then' and `else'? Lisp does just fine without them.

>>43
No, there is no need for it. It just looks nice.

Satori

48 Name: Anonymous 2011-02-04 13:36

49 Name: Sgt.Kabu竟늈kimanࠪ 2012-05-29 0:29

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