BZOJ4318: OSU!

题解戳这里…大爷传送门
http://blog.csdn.net/PoPoQQQ/article/details/49512533

#include<cstdio>#include<cstring>#include<iostream>#include<algorithm>//by:MirrorGrayusing namespace std;const int N=211111;long double dp[N],f[N][3];int main(){    int n;scanf("%d",&n);    for(int i=1;i<=n;i++)    {        double p;scanf("%lf",&p);        f[i][1]=( f[i-1][1]+1 )*p;        f[i][2]=( f[i-1][2]+(f[i-1][1]*2+1) )*p;        dp[i]=dp[i-1]+( (3*f[i-1][2]+3*f[i-1][1]+1) )*p;    }    printf("%.1f\n",(double)dp[n]);    return 0;}