省选专练之HNOI2008遥远的行星

少见的模糊DP

发现误差允许很大

可以模糊着做，不暴力算

#include<bits/stdc++.h>
using namespace std;
const int N=2e5+100;
double m[N];
double F[N];
int sum[N];
double a;
int n;
int main(){
//	freopen("test.in","r",stdin);
    scanf("%d%lf",&n,&a);
    for(int i=1;i<=n;++i){
        scanf("%lf",&m[i]);
        sum[i]=sum[i-1]+m[i];
    }
    for(int i=1;i<=n;++i){
        double now=a*i;
        int Lim=floor(now);
        if(Lim<=100){
            for(int j=1;j<=Lim;++j){
                F[i]+=(m[i]*m[j])/((double)i-(double)j);
            }
        }
        else{
            int bac=Lim/100;
            for(int j=bac;j<=bac*100;j+=bac){
                double mid=(i-j+i-j+bac-1)*0.5;
                F[i]+=(sum[j]-sum[j-bac])*m[i]/mid;
            }
            for(int j=bac*100+1;j<=Lim;++j){
                F[i]+=(m[i]*m[j])/((double)i-j);
            }
        }
        printf("%.12lf\n",F[i]);
    }
}