【Project Euler】【Problem 10】Summation of primes

Summation of primes

Problem 10

The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.

Find the sum of all the primes below two million.

Answer: 142913828922

翻译

质数的和

问题 10

10以内所有质数的和是： 2 + 3 + 5 + 7 = 17.

求2000000以内所有质数的和。

答案: 142913828922

解法一：

#include <stdio.h>
#include <math.h>

bool isPrime(long num)
{
    int _sqrt = (long)sqrt(num);

    if (num == 2 || num == 3)
    {
        return true;
    }

    for (int i = 2; i <= _sqrt; i++ )
    {
        if (num % i == 0)
        {
            return false;
        }
    }
    return true;
}


int main(int argc, char *argv[])
{
	long long result = 0;
	long maxNum = 2000000;
	int _count = 1;
	for (long i = 2; i<maxNum; i++)
	{
		if (isPrime(i))
		{
			result += i;
			_count++;
		}
	}
	printf("result is %I64d \n",result);
	return 0;
}