【杭电acm】1262 寻找素数对

 1 #include <stdio.h>
 2 #include <string.h>
 3 
 4 #define MAXNUM 10001
 5 
 6 int isPrime[MAXNUM];
 7 
 8 int main() {
 9     int i, j, tmp, sum;
10     char ch;
11 
12     memset(isPrime, 1, sizeof(isPrime));
13     isPrime[0] = isPrime[1] = 0;
14 
15     for (i=2; i<MAXNUM; ++i) {
16         if (isPrime[i]) {
17             for (j=i+i; j<MAXNUM; j=j+i)
18                 isPrime[j] = 0;
19         }
20     }
21 
22     while (scanf("%d%c", &sum, &ch) != EOF) {
23         tmp = sum / 2;
24         i = j = tmp;
25         while (i>=2 && j<sum) {
26             while (i>=2 && isPrime[i]==0)
27                 i--;
28             while (j<sum && isPrime[j]==0)
29                 j++;
30             if (i+j == sum)
31                 break;
32             if (i+j < sum)
33                 j++;
34             else
35                 i--;
36         }
37         printf("%d %d\n", i, j);
38 
39         if (ch == ‘\n‘)
40             break;
41     }
42 
43     return 0;
44 }