HDU 2993 MAX Average Problem（斜率DP经典+输入输出外挂）

 1 #include<iostream>
 2 #include<cstring>
 3 #include<algorithm>
 4 #include<stdio.h>
 5 using namespace std;
 6 const int N=1e5+5;
 7 
 8 int q[N],head,tail;
 9 long long sum[N];
10 
11 double Slope(int k,int j){
12     return double(sum[j]-sum[k])/(j-k);
13 }
14 //输入输出外挂 
15 const int BUF=25000000;
16 char Buf[BUF],*buf=Buf;
17 template <class T>
18 inline void read(T &a){
19     for(a=0;*buf<48;buf++);
20     while(*buf>47)
21         a=a*10+*buf++-48;
22 }
23 
24 int main(){
25     int n,k;
26     int tot=fread(Buf,1,BUF,stdin);
27     while(1){
28         if(buf-Buf+1>=tot)break;
29         read(n),read(k);
30         for(int i=1;i<=n;i++){
31             read(sum[i]);
32             sum[i]+=sum[i-1];
33         }
34         double ans=0;
35         head=tail=0;
36         q[tail++]=0;
37         for(int i=k;i<=n;i++){
38             while(head+1<tail&&Slope(q[head],i)<=Slope(q[head+1],i)){
39                 head++;
40             }
41             ans=max(ans,Slope(q[head],i));
42             int j=i-k+1;
43             while(head+1<tail&&Slope(q[tail-2],q[tail-1])>=Slope(q[tail-1],j)){
44                 tail--;
45             }
46             q[tail++]=j;
47         }
48         printf("%.2f\n",ans);
49     }
50     return 0;
51 }