【HDOJ6217】BBP Formula（公式）

题意：给定一个无穷项的分式，它的和等于π，问π的十六进制表示的小数点后第n位是多少

1 ≤ n ≤ 100000

思路：From https://blog.csdn.net/meopass/article/details/78327614

C++double写起来细节真是烦

 #include<cstdio>
 #include<cstring>
 #include<string>
 #include<cmath>
 #include<iostream>
 #include<algorithm>
 #include<map>
 #include<set>
 #include<queue>
 #include<vector>
 using namespace std;
 typedef long long ll;
 typedef unsigned int uint;
 typedef unsigned long long ull;
 typedef pair<int,int> PII;
 typedef vector<int> VI;
 #define fi first
 #define se second
 #define MP make_pair
 #define N   11000
 #define M   41
 #define eps 1e-8
 #define pi acos(-1)

 int read()
 {
    int v=,f=;
    char c=getchar();
    while(c<||<c) {if(c=='-') f=-; c=getchar();}
    while(<=c&&c<=) v=(v<<)+v+v+c-,c=getchar();
    return v*f;
 }

 ll Pow(ll a,ll b,ll MOD)
 {
     ll ans=;
     while(b)
     {
         if(b&) ans=ans*a%MOD;
         a=a*a%MOD;
         b>>=;
     }
     return ans;
 }

 double BBP(int n,ll k,ll b)
 {
     double ans=;
     for(int i=;i<=n;i++) ans+=(Pow(,n-i,*i+b)*1.0/(*i+b));
     for(int i=n+;i<=n+;i++) ans+=(powf(,n-i)/(*i+b));
     return k*ans;
 }

 int main()
 {
     //freopen("hdoj6217.in","r",stdin);
     //freopen("hdoj6217.out","w",stdout);
     int cas;
     scanf("%d",&cas);
     for(int v=;v<=cas;v++)
     {
         int n;
         scanf("%d",&n);
         n--;
         double ans=0.0;
         ans=BBP(n,,)+BBP(n,-,)+BBP(n,-,)+BBP(n,-,);
         ans-=int(ans);
         if(ans<) ans++;
         ans*=;
         char ch;
         int p=int(ans);
         if(<=p&&p<=) ch=p+'';
          else if(p==) ch='A';
          else if(p==) ch='B';
          else if(p==) ch='C';
          else if(p==) ch='D';
          else if(p==) ch='E';
          else if(p==) ch='F';
         printf("Case #%d: %d %c\n",v,n+,ch);

     }
     return ;
 }