hdu 4336 Card Collector

概率+状态dp

#include <CSTDIO>
#include <STRING.H>
#include <MATH.H>
// hdu 4336
/*
*/
const int MAXN = 21;
int n;
double dp[1<<MAXN], p[MAXN];
int main()
{
#ifndef ONLINE_JUDGE
freopen("in.txt", "r", stdin);
#endif
int i, j;
double pz; // 一张都没有的概率
while (scanf("%d", &n) == 1)
{
for (i = 0, pz = 0.0; i < n; ++i)
scanf("%lf", &p[i]), pz += p[i];
pz = 1 - pz;
dp[(1<<n)-1] = 0.0; // 卡片全满
int t = 1<<n;
double a, b;
for (i = t - 2 ; i >= 0; --i)
{
a = 1.0;
b = pz;
for (j = 0; j<n; ++j)
{
if ( i & (1<<j))
b += p[j];
else
a += p[j] * dp[i | (1<<j)];
}
b = 1 - b;
dp[i] = a/b;
}
printf("%.6lf\n", dp[0]);
}
return 0;
}