[Haskell-cafe] Project Euler Problem 357 in Haskell
mukesh tiwari
mukeshtiwari.iiitm at gmail.com
Tue Nov 8 14:46:23 CET 2011
Thank you Ryan . I never compiled my program with -O3 option before and
now i can feel the power of compiler optimisation.
Regards
Mukesh Tiwari
On Tue, Nov 8, 2011 at 6:50 PM, Ryan Yates <fryguybob at gmail.com> wrote:
> 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
> >>
> >>
> >> _______________________________________________
> >> Haskell-Cafe mailing list
> >> Haskell-Cafe at haskell.org
> >> http://www.haskell.org/mailman/listinfo/haskell-cafe
> >>
> >>
> >
>
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