25 lines
623 B
C++
25 lines
623 B
C++
#include <iostream>
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#include <iomanip>
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#include <cmath>
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using namespace std;
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int main()
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{
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int N,M;
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double p,q,rate,k;
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while(cin>>N>>M>>p>>q)
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{
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if(N==0){cout<<"0.00"<<endl;continue;}
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if(M==0){cout<<"1.00"<<endl;continue;}
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if(p==0||q==1){cout<<"0.00"<<endl;continue;}
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if(q==0||p==1){cout<<"1.00"<<endl;continue;}
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if(p==q) rate=1.0*N/(M+N);
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else
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{
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k = q*(1-p)/(p*(1-q));
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rate = (1.0-pow(k,N))/(1.0-pow(k,M+N));
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}
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cout<<fixed<<setprecision(2)<<rate<<endl;
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}
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return 0;
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}
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