25 lines
652 B
C++
25 lines
652 B
C++
#include<stdio.h>
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#include<math.h>
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int N, P, Q;
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double f[200005];
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double logC(int n, int m) {
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return f[n]-f[m]-f[n-m];
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}
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int main() {
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int test = 0;
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for(int i=1; i<=200000; i++)
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f[i] = f[i-1] + log(0.0+i);
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while(scanf("%d%d%d", &N, &P, &Q) != EOF) {
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double a = 0, b = 0;
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for(int red=Q; red<=N-(P-Q); red++) {
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int blue = N - red;
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double p = exp(logC(red, Q) + logC(N-red, P - Q) - logC(N, P));
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double q = (red - Q + 0.0) / (N - P);
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a += p * q;
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b += p;
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}
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printf("Case %d: %.4lf\n", ++test, a/b);
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}
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return 0;
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}
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