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.}