[題解]（單調隊列dp）luogu_P1725琪露諾

#include<bits/stdc++.h>
using namespace std;
const int maxn=200010;
int n,l,r,a[maxn];
int q[maxn],head=1,tail=0;
int f[maxn];
int main()
{
    scanf("%d%d%d",&n,&l,&r);
    for(int i=0;i<=n;i++)scanf("%d",&a[i]);
    for(int i=l;i<=n;i++){
        while(head<=tail && q[head]+r<i)head++;
        while(head<=tail && f[q[tail]]<f[i-l])tail--;
        q[++tail]=i-l;//不能直接用i,不然記個p當做時間也行(一樣效果 
        f[i]=f[q[head]]+a[i];
    }
    int ans=0;
    for(int i=n+1-r;i<=n;i++)ans=max(ans,f[i]);
    printf("%d",ans);
}