一本通1599：修剪草坪

#include <iostream>
using namespace std;
 const int N=2e5+3;
 
 #define int long long
 int a[N],s[N],f[N][2],n,m;
 int hh,tt,q[N];
 
 int func(int j){
     return f[j][0]-s[j];
 }
 void solve(){
     int i,j;
     hh=tt=1;
     for(i=1;i<=n;i++){
         f[i][0]=max(f[i-1][0],f[i-1][1]);
         while(hh<=tt&&q[hh]<i-m) hh++;
         
         f[i][1]=func(q[hh])+s[i];
         while(hh<=tt&&func(i)>func(q[tt])) tt--;
         q[++tt]=i;
     }
     cout<<max(f[n][0],f[n][1]);
 }
 main(){
     cin>>n>>m;
    for(int i=1;i<=n;i++) cin>>a[i],s[i]=s[i-1]+a[i];
     solve();
 }