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);