hdu 2993 最大區間平均值

#include<stdio.h>
#include<iostream>
#include<string.h>
#include<queue>
#include<algorithm>
using namespace std;
const int MAXN=100010;
double sum[MAXN];
int a[MAXN];
int q[MAXN];
int head,tail;

double max(double a,double b)
{
    if(a>b)return a;
    else return b;
}

double getUP(int i,int j)//i>j
{
    return sum[i]-sum[j];
}
int getDOWN(int i,int j)
{
    return i-j;
}



inline int input()
{
    char ch=' ';
    while(ch<'0'||ch>'9')ch=getchar();
    int x=0;
    while(ch<='9'&&ch>='0')x=x*10+ch-'0',ch=getchar();
    return x;
}

int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    int n,k;
    while(scanf("%d%d",&n,&k)!=EOF)
    {
        sum[0]=0;
        for(int i=1;i<=n;i++)
        {
           scanf("%d",&a[i]);
            sum[i]=sum[i-1]+a[i];
        }
        head=tail=0;
        q[tail++]=0;
        double ans=0;
        for(int i=k;i<=n;i++)
        {
            while(head+1<tail&&getUP(i,q[head])*getDOWN(i,q[head+1])<=getUP(i,q[head+1])*getDOWN(i,q[head]))
              head++;
            ans=max(ans,getUP(i,q[head])/getDOWN(i,q[head]));

            int j=i-k+1;
            while(head+1<tail&&getUP(j,q[tail-1])*getDOWN(q[tail-1],q[tail-2])<=getUP(q[tail-1],q[tail-2])*getDOWN(j,q[tail-1]))
                 tail--;
            q[tail++]=j;

        }
        printf("%.2lf\n",ans);
    }
    return 0;
}