# [Haskell-cafe] Project Euler Problem 357 in Haskell

Ryan Yates fryguybob at gmail.com
Tue Nov 8 14:20:37 CET 2011

```I forgot to add, I'm on 32-bit GHC and the sum will overflow there, so
I changed main:

main = putStrLn . show . sum  \$ ([ if and [ pList ! i , divPrime .
pred \$ i ] then (fromIntegral \$ pred i) else 0 | i <- [ 2 .. 10 ^ 8 ]
] :: [Integer])

On Tue, Nov 8, 2011 at 8:19 AM, Ryan Yates <fryguybob at gmail.com> wrote:
> If I compile with optimizations:
>
> ghc --make -O3 primes.hs
>
> I get an answer that is off by one from the C++ program in a few seconds.
>
>
> On Tue, Nov 8, 2011 at 7:46 AM, mukesh tiwari
> <mukeshtiwari.iiitm at gmail.com> wrote:
>> In that loop , I  am collecting all the primes in vector how ever I changed
>> the c++ code and  now it resembles to Haskell code. This code  still gives
>> the answer within a second.
>>
>> #include<cstdio>
>> #include<iostream>
>> #include<vector>
>> #define Lim 100000001
>> using namespace std;
>>
>> bool prime [Lim];
>> vector<int> v ;
>>
>> void isPrime ()
>>      {
>>         for( int i = 2 ; i * i <= Lim ; i++)
>>          if ( !prime [i]) for ( int j = i * i ; j <= Lim ; j += i ) prime
>> [j] = 1 ;
>>
>>         //for( int i = 2 ; i <= Lim ; i++) if ( ! prime[i] ) v.push_back( i
>> ) ;
>>         //cout<<v.size()<<endl;
>>         //for(int i=0;i<10;i++) cout<<v[i]<<" ";cout<<endl;
>>
>>      }
>>
>> int main()
>>     {
>>         isPrime();
>>         int n = v.size();
>>         long long sum = 0;
>>         for(int i = 0 ; i < Lim ; i ++)
>>          if ( ! prime [i])
>>          {
>>             int k = i-1;
>>             bool f = 0;
>>             for(int i = 1 ; i*i<= k ; i++)
>>                 if ( k % i == 0 && prime[ i + ( k / i ) ] )  { f=1 ; break ;
>> }
>>
>>             if ( !f ) sum += k;
>>          }
>>         cout<<sum<<endl;
>>     }
>>
>> Regards
>> Mukesh Tiwari
>>
>> On Tue, Nov 8, 2011 at 6:03 PM, Ivan Lazar Miljenovic
>> <ivan.miljenovic at gmail.com> wrote:
>>>
>>> On 8 November 2011 23:29, mukesh tiwari <mukeshtiwari.iiitm at gmail.com>
>>> wrote:
>>> >> Also, I'm not sure if the logic in the two versions is the same: I'm
>>> >> not sure about how you handle the boolean aspect in C++, but you have
>>> >> a third for-loop there that doesn't seem to correspond to anything in
>>> >> the Haskell version.
>>> >>
>>> > Which  loop ?
>>>
>>> for( int i = 2 ; i <= Lim ; i++) if ( ! prime[i] ) v.push_back( i ) ;
>>>
>>> --
>>> Ivan Lazar Miljenovic
>>> Ivan.Miljenovic at gmail.com
>>> IvanMiljenovic.wordpress.com
>>
>>
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>>
>>
>

```

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