洛谷p1725 露琪诺 单调队列优化的DP

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
int n,L,R,a[400007];
const int INF=2e8+7;
int dfs(int pos){
    if(pos>n) return 0;
    int i,k=-INF;
    for(i=pos+L;i<=pos+R;++i){
        k=max(k,dfs(i));
    }
    return k+a[pos];
}
int dp[400007],q[400007],head,tail,l,r;
void solve(){
    int i,j;head=0,tail=0;
    memset(dp,0,sizeof(dp));
    l=n+R+1,r=n+R+1;
    //固定r移动l
    for(i=n;i>=0;--i){
        // dp[i]=-INF;
        // for(j=i+L;j<=i+R;++j){
        //     dp[i]=max(dp[i],dp[j]);
        // }
        // dp[i]+=a[i];
        r--;
        while(head!=tail&&q[head]>i+R) head++;
        while(r-l+1<R-L+1){
            l--;
            if(head==tail){
                q[tail++]=l;
            }
            else{
                while(head!=tail&&dp[q[tail-1]]<=dp[l]) tail--;
                q[tail++]=l;
            }
        }
        dp[i]=dp[q[head]]+a[i];//少加了dp
    }
}
int main(){
    while(~scanf("%d%d%d",&n,&L,&R)){
        memset(a,0,sizeof(a));
        int i;
        for(i=0;i<=n;++i) scanf("%d",a+i);
        solve();
        printf("%d\n",dp[0]);
    }
    return 0;
}