前缀和

运用前缀和，求解：

#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 9;
int n, k, ans, s[N];

int main() {
    cin >> n;
    cin >> k;
    for (int i = 1; i <= n; i++) {
        int x;
        cin >> x;
        s[i] = s[i - 1] + x;
    }
    for (int i = 1; i <= n - k; i++) {
        ans = max(ans, s[i + k] - s[i - 1]);
    }
    cout << ans;
    return 0;
}