原题链接

#include<iostream>
#include<climits>
using namespace std;
typedef long long LL;

int n, m;
const int N = 300010;
int q[N], tt = 0, hh = 0;
LL s[N];

int main(){
    cin >> n >> m;
    for(int i = 1; i <= n; ++i) cin >> s[i], s[i] = s[i - 1] + s[i];
    LL res = INT_MIN;
    for(int i = 1; i <= n; ++i)
    {
        if(i - q[hh] > m) hh++;
        res = max(res, s[i] - s[q[hh]]);
        while(hh <= tt && s[q[tt]] >= s[i]) tt--;
        q[++tt] = i;
    }
    cout << res << endl;
    return 0;
}