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  • UVA 1639 Candy

    #include<bits/stdc++.h>
    #include<stdio.h>
    #include<iostream>
    #include<cmath>
    #include<math.h>
    #include<queue>
    #include<set>
    #include<map>
    #include<iomanip>
    #include<algorithm>
    #include<stack>
    #define inf 0x3f3f3f3f
    using namespace std;
    typedef long long ll;
    long double ln_fac[400051];
    long double ln_C(int n,int m)
    {
        long double res=ln_fac[n]-ln_fac[m]-ln_fac[n-m];
        return res;
    }
    int n;double p;
    double ans=0;
    int id=1;
    int main()
    {
    #ifndef ONLINE_JUDGE
        freopen("in.txt","r",stdin);
    #endif // ONLIN23
        ln_fac[1]=log(1);
        for(int i=2;i<=400050;i++)ln_fac[i]=ln_fac[i-1]+log(i);
        long double tmp;
        while(cin>>n>>p)
        {
            if(fabs(p)<0.000000001||fabs(p-1)<0.000000001){printf("Case %d: %.6f
    ",id++,(double)n);continue;}
            ans=0;
            for(int i=0;i<=n;i++)
            {
                tmp=ln_C(2*n-i,n)+(n+1)*log(p)+(n-i)*log(1-p);
                ans+=i*exp(tmp);
                tmp=ln_C(2*n-i,n)+(n+1)*log(1-p)+(n-i)*log(p);
                ans+=i*exp(tmp);
            }
            printf("Case %d: %.6f
    ",id++,ans);
        }
    
    }
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  • 原文地址:https://www.cnblogs.com/linruier/p/9532570.html
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