如题
记录

#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'
const int mod = 1e9 + 7;
const int INF = 0x3f3f3f3f;
const int N = 3e5 + 10;

void solve() {
	int n, k;
	cin >> n >> k;
	vector<int>a(2 * n + 1, 0);
	int mx = -2e9;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
		mx = max(mx, a[i]);
		a[i] += a[i - 1];//前缀和
	}
	for (int l = 1, r = 1; r <= n; r++) {
		int res = a[r] - a[l - 1];
		mx = max(mx, res);
		if (res < 0 && l < r) {//区间和为负数就把l往r移动
			while (l <= r && res < 0) {
				res = a[r] - a[l - 1];
				mx = max(mx, res);
				l++;
			}
		}
		if (a[l] - a[l - 1] < 0 && l < r) {//如果l位于负数就往r移动
			while (a[l] - a[l - 1] < 0 && l <= r) {
				l++;
				res = a[r] - a[l - 1];
				mx = max(mx, res);
			}
		}
		if (r - l + 1 >= k) {
			l++;
			res = a[r] - a[l - 1];
			mx = max(mx, res);
		}
		mx = max(mx, res);
		if (r == n) {
			while (l < r) {
				l++;
				res = a[r] - a[l - 1];
				mx = max(mx, res);
			}
		}
	}
	cout << mx;
}

signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int t = 1;
	while (t--)
		solve();
	return 0;
}