HDU 2993 MAX Average Problem (斜率优化)

#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;
}

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]);
a[i]=input();
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;
}