# project euler #10: optimization with primes

Michael P. baseball.mjp at gmail.com
Tue Mar 31 18:11:45 PDT 2009

```Hey, I've started to do some of the problems on Project Euler to practice my programming skills. I'm doing #10 right now, and I think I've got a working solution. It's just that it's way too slow.
http://projecteuler.net/index.php?section=problems&id=10
The code works fine with sum of primes below 10. It output 17.
But for 2 million, it takes quite a while, and an FAQ on the page said most problems are made with being run within a minute. Mine was gonna quite a bit longer.
Here is my code:

//Import
import std.stdio;
import std.math;

//Main
int main()
{
int sum = 2;
long bigNum = 10; //Or 2 million
for ( int i = 3; i < bigNum; i += 2 )
{
if( isPrime( i ) )
{
sum += i;
}
}
writefln( sum );
return 0;
}

//Functions
bool isPrime( long n )
{
for( int i = 2; i < n; i++ )
{
if ( n % i == 0 )
{
return false;
}
}
return true;
}

I'm pretty sure the isPrime() function can be done better.
```