B. Lecture Sleep（ Educational Codeforces Round 41 (Rated for Div. 2)）

 1 #include <iostream>
 2 #include <algorithm>
 3 using namespace std;
 4 
 5 const int maxn = 1e5 + 5;
 6 int a[maxn], f[maxn], b[maxn], c[maxn];
 7 
 8 int main()
 9 {
10     ios::sync_with_stdio(false);
11     int n, k;
12     cin >> n >> k;
13     for (int i = 1; i <= n; i++)
14         cin >> a[i];
15     for (int i = 1; i <= n; i++)
16         cin >> f[i];
17     //前缀和
18     for (int i = 1; i <= n; i++)
19     if (f[i])b[i] = b[i - 1] + a[i];
20     else b[i] = b[i - 1];
21     //后缀和
22     for (int i = n; i>0; i--)
23     if (f[i])c[i] = c[i + 1] + a[i];
24     else c[i] = c[i + 1];
25 
26     long long s = 0;
27     for (int i = 1; i <= k; i++)s += a[i];
28     long long ans = 0;
29     for (int i = k; i <= n; i++){
30         ans = max(b[i - k] + s + c[i + 1], ans);
31         s = s - a[i - k + 1] + a[i + 1];
32     }
33     cout << ans;
34     return 0;
35 }