POJ 2262 Goldbach's Conjecture

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 using namespace std;
 5 #define N 1000005
 6 
 7 bool prime[N];//int会超内存
 8 
 9 void dabiao()//筛法求素数
10 {
11     int i,j;
12     prime[0]=prime[1]=1;
13 
14     for (i=2;i<N;i++)
15     {
16         if (!prime[i])
17         {
18             for (j=2*i;j<N;j+=i)
19             {
20                 prime[j]=1;
21             }
22         }
23     }
24 }
25 
26 void test()
27 {
28     int i;
29     for (i=0;i<N;i++)
30     {
31         printf("%2d",prime[i]);
32     }
33 }
34 
35 int main()
36 {
37     int n,i;
38     dabiao();
39 //    test();
40 
41     while (scanf("%d",&n)&&n)
42     {
43         for (i=1;i<=n/2;i++)//到n/2即可
44         {
45             if (!prime[i]&&!prime[n-i])
46             {
47                 printf("%d = %d + %d\n",n,i,n-i);
48                 break;
49             }
50         }
51     }
52 
53     return 0;
54 }