poj1992 数论

 1 //Accepted    168 KB    969 ms
 2 //n!中含有质因数p的个数为t=n/p+n/p^2+n/p^3+...
 3 #include <cstdio>
 4 #include <cstring>
 5 #include <iostream>
 6 using namespace std;
 7 const int imax_n = 435;
 8 int pri[imax_n];
 9 void prime()
10 {
11     for (int i=2;i<imax_n;i++)
12     {
13         for (int j=i*i;j<imax_n;j+=i)
14         {
15             pri[j]=1;
16         }
17     }
18 }
19 int getNumber(int n,int k)
20 {
21     int ans=0;
22     while (n>0)
23     {
24         ans+=n/k;
25         n=n/k;
26     }
27     return ans;
28 }
29 void slove(int n,int k)
30 {
31     __int64 ans=1;
32     for (int i=2;i<=n;i++)
33     if (pri[i]==0)
34     {
35        int t=getNumber(n,i)-getNumber(k,i)-getNumber(n-k,i)+1;
36        ans*=t;
37     }
38     printf("%I64d\n",ans);
39 }
40 int main()
41 {
42     prime();
43     int n,k;
44     while (scanf("%d%d",&n,&k)!=EOF)
45     {
46         slove(n,k);
47     }
48     return 0;
49 }

 1 //Accepted    900 KB    344 ms
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <iostream>
 5 using namespace std;
 6 const int imax_n = 435;
 7 int pri[imax_n];
 8 int a[imax_n][imax_n];
 9 void prime()
10 {
11     for (int i=2;i<imax_n;i++)
12     {
13         for (int j=i*i;j<imax_n;j+=i)
14         {
15             pri[j]=1;
16         }
17     }
18 }
19 int getNumber(int n,int k)
20 {
21     int ans=0;
22     while (n>0)
23     {
24         ans+=n/k;
25         n=n/k;
26     }
27     return ans;
28 }
29 void getA()
30 {
31     for (int i=0;i<=431;i++)
32     {
33         for (int j=2;j<=431;j++)
34         {
35             if (pri[j]==0)
36             a[i][j]=getNumber(i,j);
37         }
38     }
39 }
40 void slove(int n,int k)
41 {
42     __int64 ans=1;
43     for (int i=2;i<=n;i++)
44     if (pri[i]==0)
45     {
46         //printf("a[%d][%d]=%d\n",n,i,a[n][i]);
47         //printf("a[%d][%d]=%d\n",k,i,a[k][i]);
48         //printf("a[%d][%d]=%d\n",n-k,i,a[n-k][i]);
49        int t=a[n][i]-a[k][i]-a[n-k][i]+1;
50        ans*=t;
51     }
52     printf("%I64d\n",ans);
53 }
54 int main()
55 {
56     prime();
57     getA();
58     int n,k;
59     while (scanf("%d%d",&n,&k)!=EOF)
60     {
61         slove(n,k);
62     }
63     return 0;
64 }