UVa 294 (因数的个数) Divisors

 1 #include <cstdio>
 2 #include <cmath>
 3 
 4 const int maxn = 31700;
 5 bool vis[maxn + 10];
 6 int prime[3450], cnt = 0;
 7 
 8 void Init()
 9 {
10     int m = sqrt(maxn + 0.5);
11     for(int i = 2; i <= m; ++i) if(!vis[i])
12         for(int j = i * i; j <= maxn; j += i) vis[j] = true;
13     for(int i = 2; i <= maxn; ++i) if(!vis[i]) prime[cnt++] = i;
14 }
15 
16 int factor_number(int n)
17 {
18     int m = sqrt(n + 0.5);
19     int ans = 1;
20     for(int i = 0; prime[i] <= m; ++i)
21     {
22         int k = 1;
23         while(n % prime[i] == 0)
24         {
25             k++;
26             n /= prime[i];
27         }
28         ans *= k;
29     }
30     if(n > 1) ans <<= 1;
31     return ans;
32 }
33 
34 int main()
35 {
36     Init();
37     int a, b, T;
38     scanf("%d", &T);
39     while(T--)
40     {
41         scanf("%d%d", &a, &b);
42         int ans, temp = 0;
43         for(int i = a; i <= b; ++i)
44         {
45             int k = factor_number(i);
46             if(k > temp) { temp = k; ans = i; }
47         }
48         printf("Between %d and %d, %d has a maximum of %d divisors.\n", a, b, ans, temp);
49     }
50 
51     return 0;
52 }