Submission #20

#include <iostream>
#include <vector>
#include <deque>
#include <climits>
using namespace std;
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, k;
    cin >> n >> k;
    vector<long long> A(n);
    for (int i = 0; i < n; i++){
        cin >> A[i];
    }
    vector<long long> dp(n, LLONG_MIN);
    dp[0] = A[0];
    deque<int> dq;
    dq.push_back(0);
    for (int i = 1; i < n; i++){
        while (!dq.empty() && dq.front() < i - k)
            dq.pop_front();
        dp[i] = A[i] + dp[dq.front()];
        while (!dq.empty() && dp[dq.back()] <= dp[i])
            dq.pop_back();
        dq.push_back(i);
    }
    cout << dp[n - 1];
    return 0;
}