hdu 2993 斜率dp

思路：直接通过斜率优化进行求解。

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<cstring>
#define Maxn 1000010
using namespace std;
__int64 sum[Maxn];
__int64 num[Maxn];
int que[Maxn*4];
int main()
{
    int n,k,head,rear,x;
    int i,j;
    double ans;
    while(scanf("%d%d",&n,&k)!=EOF){
        ans=0;
        for(i=1;i<=n;i++){
            scanf("%I64d",&num[i]);
            sum[i]=sum[i-1]+num[i];
        }
        head=1,rear=0;
        que[++rear]=0;
        for(i=k;i<=n;i++){
            j=i-k+1;
            while(head<rear&&(sum[i]-sum[que[head+1]])*(i-que[head])>=(sum[i]-sum[que[head]])*(i-que[head+1]))
                head++;
            ans=max(ans,(double)((double)sum[i]-(double)sum[que[head]])/(double)((double)i-(double)que[head]));
            while(head<rear&&(sum[j]-sum[que[rear]])*(que[rear]-que[rear-1])<=(sum[que[rear]]-sum[que[rear-1]])*(j-que[rear]))
                rear--;
            que[++rear]=j;
        }
        printf("%.2lf\n",ans);
    }
    return 0;
}