31 lines
645 B
C++
31 lines
645 B
C++
#include<stdio.h>
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#include<string.h>
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#include<math.h>
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#define N 400200
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double f[N];
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double logc(int n,int m)
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{
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return f[m]-f[n]-f[m-n];
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}
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int main ()
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{
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int n;
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int i,j,k=0;
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double p,ans,ret;
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f[0]=0;
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for (i=1;i<N;++i) f[i]=f[i-1]+log(1.0*i);
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while (scanf("%d%lf",&n,&p)!=EOF)
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{
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ans=0;
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double p1=log(p),p2=log(1-p);
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double q1=(n+1)*p1,q2=(n+1)*p2;
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for (i=0;i<n;++i)
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{
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ans+=((n-i)*exp(logc(n,n+i)+q1+i*p2));
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ans+=((n-i)*exp(logc(n,n+i)+q2+i*p1));
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}
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printf("Case %d: %.6lf\n",++k,ans);
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}
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return 0;
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}
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