AcWing 135 最大子序和

#include <bits/stdc++.h>
using namespace std;

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    
    int n, m;
    cin >> n >> m;
    
    vector<int> a(n + 1);
    for (int i = 1; i <= n; i ++ )
    {
        cin >> a[i];
        a[i] += a[i - 1];
    }
    
    vector<int> q(n + 1);
    int res = INT_MIN, hh = 0, tt = 0;
    for (int i = 1; i <= n; i ++ )
    {
        if (q[hh] < i - m) hh ++;
        res = max(res, a[i] - a[q[hh]]);
        while (hh <= tt && a[q[tt]] > a[i]) tt --;
        q[ ++ tt] = i;
    }
    
    cout << res << endl;
    
    return 0;
}