P2115 [USACO14MAR]破坏Sabotage

实数二分6的一批
QAQ
设前缀和为 S，则去掉 [i,j] 的平均值为
(S[n]-(S[j]-S[i-1])) / (n-(j-i+1)) <= X
S[n] − S[j] + S[i − 1] <= Xn − Xj + X(i − 1)
(S[n] − Xn) − (S[j] − Xj) + (S[i − 1] − X(i − 1)) <= 0
S[i-1]-X(i-1)维护最小值即可。
注意不要删去最后和最前面的机器

#include 
#include 
#include 
#include 
#define ll long long
#define db double 
using namespace std;
db a[999999],sum[999999];
db n;
bool check(db mid)
{
    int t=n;
    db nowmin=sum[1]-mid;
    db x=sum[t]-mid*n;
    for(int i=2;iif(x-(sum[i]-mid*i)+nowmin<=0) return 1;
        nowmin=min(nowmin,sum[i]-mid*i);
    }
    return 0;
}
int main()
{
      scanf("%lf",&n);
      for(int i=1;i<=n;i++)
       scanf("%lf",a+i),sum[i]=sum[i-1]+a[i];
      db l=0,r=1e7;
      db ans=0;
      while(r-l>1e-5) 
      {
        db mid=(l+r)/2.0;
        if(check(mid)) r=mid;
        else l=mid;
      }
      printf("%.3lf",r);
}