luoguP1419 寻找段落(二分答案+单调队列）

#include<iostream>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<cstdio>
using namespace std;
const int N=100000;
int n,a[N],q[N],s,t;
double ans,mid,l,r,sum[N],b[N];
bool judge(double pi){
    for(int i=1;i<=n;i++){
        b[i]=(double)a[i]-pi;
    }
//    cout<<pi<<endl;
    for(int i=1;i<=n;i++){
        sum[i]=sum[i-1]+b[i];
    //    cout<<sum[i]<<" ";
    }
//    cout<<endl;
    int head=1;
    int tail=0;
    for(int i=s;i<=n;i++){
        while(q[head]+t-1<i&&head<=tail)head++;
        while(sum[i-s]<sum[q[tail]]&&head<=tail)tail--;
        q[++tail]=i-s;
        if(head<=tail&&sum[i]-sum[q[head]]>=0)return true;
    }
    return false;
}
int main(){
    scanf("%d%d%d",&n,&s,&t);
    for(int i=1;i<=n;i++){
        scanf("%d",&a[i]);
    }
    ans=-10000.0;
    l=-10000.0;r=10000.0;
    while(r-l>=1e-5){
        mid=(l+r)/2;
        if(judge(mid)){
            ans=mid;
            l=mid+1e-5;
        }
        else r=mid-1e-5;
    }
    printf("%.3lf",ans);
    return 0;
}