欧拉计划 第10题

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

Find the sum of all the primes below two million.

 

?

int[] numbers = Enumerable.Range(1, 2000000).ToArray();

int prime = 2;

int nextPrime = 2;

int nextPrimePow2 = 2 * 2;

for (int i = 1; nextPrimePow2 < 2000000; i++)

{

    int n = numbers[i];

    if (n == 0) continue;

    for (int j = i + 1; j < numbers.Length; j++)

    {

        int k = numbers[j];

        if (k % prime == 0)

        {

            numbers[j] = 0;

            continue;

        }

        if (prime == nextPrime) nextPrime = k;

    }

    prime = nextPrime;

    nextPrimePow2 = nextPrime * nextPrime;

}

long primeSum = 0;

foreach (var item in numbers)

{

    primeSum += item;

}

Console.WriteLine(primeSum - 1);