UVa10375 Choose and divide

 1 /*by SilverN*/
 2 #include<iostream>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<cstdio>
 6 #include<cmath>
 7 using namespace std;
 8 const int mxn=12000;
 9 int pri[mxn],cnt=0;
10 bool vis[mxn];
11 int num[mxn];
12 void Pri(){
13     int m=sqrt(mxn);
14     cnt=0;int i,j;
15     for(i=2;i<=m;i++)
16         if(!vis[i])    for(j=i*i;j<mxn;j+=i)vis[j]=1;
17     for(i=2;i<mxn;i++)if(!vis[i])pri[++cnt]=i;
18 }
19 void addint(int n,int v){//n-要分解的数字 v-正负 
20     int i,j;
21     for(i=1;i<=cnt;i++){
22         while(n%pri[i]==0){
23             n/=pri[i];
24             num[i]+=v;
25         }
26         if(n==1)return;
27     }
28     return;
29 }
30 void solve(int n,int v){
31     for(int i=1;i<=n;i++)
32         addint(i,v);
33     return;
34 }
35 int main(){
36     Pri();
37     int p,q,r,s;int mx;
38     while(scanf("%d%d%d%d",&p,&q,&r,&s)!=EOF){
39         memset(num,0,sizeof num);
40         solve(p,1);
41         solve(q,-1);
42         solve(p-q,-1);
43         solve(r,-1);
44         solve(s,1);
45         solve(r-s,1);
46         mx=max(p,r);
47         double ans=1;
48         for(int i=1;i<=cnt;i++){
49             ans*=pow(pri[i],num[i]);
50         }
51         printf("%.5f\n",ans);
52     }
53     return 0;
54 }