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

前缀后缀和搞一搞，然后枚举一下区间，找出最大值

 #include <iostream>
 #include <algorithm>
 using namespace std;

 const int maxn = 1e5 + ;
 int a[maxn], f[maxn], b[maxn], c[maxn];

 int main()
 {
     ios::sync_with_stdio(false);
     int n, k;
     cin >> n >> k;
     for (int i = ; i <= n; i++)
         cin >> a[i];
     for (int i = ; i <= n; i++)
         cin >> f[i];
     //前缀和
     for (int i = ; i <= n; i++)
     if (f[i])b[i] = b[i - ] + a[i];
     else b[i] = b[i - ];
     //后缀和
     for (int i = n; i>; i--)
     if (f[i])c[i] = c[i + ] + a[i];
     else c[i] = c[i + ];

     long long s = ;
     for (int i = ; i <= k; i++)s += a[i];
     long long ans = ;
     for (int i = k; i <= n; i++){
         ans = max(b[i - k] + s + c[i + ], ans);
         s = s - a[i - k + ] + a[i + ];
     }
     cout << ans <<endl;
　　　　//system("pause");
     return ;
 }