【HDOJ】1239 Calling Extraterrestrial Intelligence Again

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <math.h>
 4 
 5 char isPrime[100001];
 6 
 7 int main() {
 8     int i, j, q, p, maxi, maxj, max;
 9     double m, a, b, n, tmp1, tmp2;
10 
11     memset(isPrime, 1, sizeof(isPrime));
12     isPrime[0] = isPrime[1] = 0;
13     for (i=2; i<100001; ++i) {
14         if (isPrime[i]) {
15             for (j=i+i; j<100001; j+=i)
16                 isPrime[j] = 0;
17         }
18     }
19 
20     while (scanf("%lf %lf %lf", &m, &a, &b) != EOF) {
21         if (m==0.0f && a==0.0f && b==0.0f)
22             break;
23         n = a/b;
24         a = sqrt(m);
25         b = sqrt(m/n);
26         i = (int)floor(a);
27         j = (int)floor(b);
28         max = 0;
29         for (p=j; p>=2; --p) {
30             if ( !isPrime[p] )
31                 continue;
32             if (p*i <= max)
33                 break;
34             for (q=i; q>=2; --q) {
35                 if ( !isPrime[q] )
36                     continue;
37                 tmp1 = p*q;
38                 tmp2 = q*1.0f/p;
39                 if (tmp1<=m && tmp2<=1 && tmp2>=n) {
40                     if (tmp1 > max) {
41                         max = tmp1;
42                         maxj = p;
43                         maxi = q;
44                     }
45                     break;
46                 }
47             }
48         }
49         printf("%d %d\n", maxi, maxj);
50     }
51 
52     return 0;
53 }