POJ-2992 Divisors(数学知识)

 1 #include "bits/stdc++.h"
 2 using namespace std;
 3 typedef long long LL;
 4 const int MAX=435;
 5 int n,m,len,pri[MAX];LL ans[MAX][MAX];
 6 bool t[MAX];
 7 void prime(){
 8     register int i,j;
 9     memset(t,true,sizeof(t));
10     for (i=2;i<MAX;i++){
11         if (t[i]) pri[++len]=i;
12         for (j=1;j<=len && pri[j]*i<MAX;j++) {t[pri[j]*i]=false; if (i%pri[j]==0) break;}
13     }
14 }
15 inline int calc(register int x,register int y){
16     register int an=0;
17     while (x){an+=x/y;x/=y;}
18     return an;
19 }
20 int main(){
21     freopen ("divisors.in","r",stdin);freopen ("divisors.out","w",stdout);
22     register int i,j,k;
23     prime();ans[0][0]=1;
24     for (i=1;i<MAX;i++){
25         ans[i][i]=ans[i][0]=1;
26         for (j=1;j<i;j++){
27             ans[i][j]=1;
28             for (k=1;k<=len;k++)
29                 ans[i][j]*=calc(i,pri[k])-calc(j,pri[k])-calc(i-j,pri[k])+1;
30         }
31     }
32     while (~scanf("%d%d",&n,&m)) printf("%lld\n",ans[n][m]);
33     return 0;
34 }