Re: [Haskell-cafe] Project Euler Problem 357 in Haskell

8 Nov 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  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
 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<
     }
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<
Regards
Mukesh Tiwari
On Tue, Nov 8, 2011 at 6:03 PM, Ivan Lazar Miljenovic
 wrote:
...
On 8 November 2011 23:29, mukesh tiwari 
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@gmail.com
IvanMiljenovic.wordpress.com
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