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 + 5;
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 = 1; i <= n; i++)
        cin >> a[i];
    for (int i = 1; i <= n; i++)
        cin >> f[i];
    //前缀和
    for (int i = 1; i <= n; i++)
    if (f[i])b[i] = b[i - 1] + a[i];
    else b[i] = b[i - 1];
    //后缀和
    for (int i = n; i>0; i--)
    if (f[i])c[i] = c[i + 1] + a[i];
    else c[i] = c[i + 1];

    long long s = 0;
    for (int i = 1; i <= k; i++)s += a[i];
    long long ans = 0;
    for (int i = k; i <= n; i++){
        ans = max(b[i - k] + s + c[i + 1], ans);
        s = s - a[i - k + 1] + a[i + 1];
    }
    cout << ans <<endl;
　　　　//system("pause");
    return 0;
}