【bzoj4008】 HNOI2015—亚瑟王

// bzoj4008
#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<cmath>
#define LL long long
#define inf 1<<30
#define Pi acos(-1.0)
#define free(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);
using namespace std;

const int maxn=500;
int d[maxn],n,r;
double p[maxn],f[maxn][maxn];

double power(double a,int b) {
	double res=1;
	while (b) {
		if (b&1) res*=a;
		b>>=1;a*=a;
	}
	return res;
}
int main() {
	int T;scanf("%d",&T);
	while (T--) {
		memset(f,0,sizeof(f));
		scanf("%d%d",&n,&r);
		for (int i=1;i<=n;i++) scanf("%lf%d",&p[i],&d[i]);
		f[0][r]=1;double ans=0;
		for (int i=1;i<=n;i++)
			for (int j=1;j<=r;j++) {
				f[i][j]=f[i-1][j]*power(1-p[i-1],j)+f[i-1][j+1]*(1-power(1-p[i-1],j+1));
				ans+=f[i][j]*(1-power(1-p[i],j))*d[i];
			}
		printf("%.10lf\n",ans);
	}
	return 0;
}