Cod sursa(job #259676)
Utilizator | Data | 15 februarie 2009 17:35:20 | |
---|---|---|---|
Problema | Dezastru | Scor | 90 |
Compilator | cpp | Status | done |
Runda | Arhiva de probleme | Marime | 0.45 kb |
#include <stdio.h>
double s=0, f[26];
int n, x, k, st[20], o=0;
void back(int k, int l, double z)
{
if (k == x)
{
o++;
s+=z;
return;
}
for (int i=l+1;i<=n-x+k;i++)
back( k + 1, i, z * f[i] );
}
int main(void)
{
freopen ("dezastru.in", "r", stdin);
freopen ("dezastru.out", "w", stdout);
scanf("%d%d", &n, &x);
for (register int i = 0;i<n;i++)
scanf("%lf", f+i);
back(0, -1, 1);
printf ("%.6lf", s/o);
return 0;
}