Problem10

1.package com.shui.mu.yao.io.algorithm;
2.
3.import java.util.ArrayList;
4.import java.util.Arrays;
5.import java.util.List;
6.
7./**
8. *
9. * @author shuimuqinghua77 @date 2011-11-3下午07:44:42
10. */
11./**
12. * The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17. Find the sum of all the
13. * primes below two million.
14. */
15.public class Problem10 {
16.    private static List<Long> seed = new ArrayList<Long>();
17.
18.    private static void initSeed(long[] seeds) {
19.        for (long i : seeds)
20.            seed.add(i);
21.    }
22.
23.    public static long sumBelowTop(long top) {
24.        initSeed(new long[] { 2 });
25.        long middle = (long) Math.sqrt(top);
26.        for (long k = 2, factor = 2, i = factor * k - 1; i < top; factor++, i = factor
27.                * k - 1) {
28.            boolean isPrime = true;
29.            for (long s : seed) {
30.                if (s > middle)
31.                    break;
32.                if (i % s == 0) {
33.                    isPrime = false;
34.                    break;
35.                }
36.
37.            }
38.            if (isPrime)
39.                seed.add(i);
40.        }
41.        long sum = 0;
42.        for (long s : seed) {
43.            sum += s;
44.        }
45.        return sum;
46.
47.    }
48.
49.    public static void main(String[] args) {
50.        long sum = sumBelowTop(2000000l);
51.        // System.out.println(Arrays.toString(seed.toArray()));
52.        System.out.println(sum);
53.    }
54.}