poj3276 Face The Right Way

思路：
枚举。前缀和优化。
实现：
 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 using namespace std;
 5 const int INF = 0x3f3f3f3f;
 6 char a[5005];
 7 int f[15555], sum[15555], n;
 8 int solve(int k)
 9 {
10     memset(f, 0, sizeof f);
11     memset(sum, 0, sizeof sum);
12     for (int i = 5005; i <= 5005 + n - k; i++)
13     {
14         int tmp = sum[i - 1] - sum[i - k];
15         if ((tmp % 2 == 0 && a[i - 5005] == 'B') || (tmp % 2 == 1 && a[i - 5005] == 'F'))
16         {
17             f[i] = 1;
18         }
19         sum[i] = sum[i - 1] + f[i];
20     }
21     for (int i = 5006 + n - k; i < 5005 + n; i++)
22     {
23         sum[i] = sum[i - 1] + f[i];
24         int tmp = sum[i - 1] - sum[i - k];
25         if ((tmp % 2 == 0 && a[i - 5005] == 'B') || (tmp % 2 == 1 && a[i - 5005] == 'F'))
26         {
27             return -1;
28         }
29     }
30     return sum[5005 + n - k];
31 }
32 int main()
33 {
34     cin >> n;
35     for (int i = 0; i < n; i++)
36     {
37         cin >> a[i];
38     }
39     int minn = INF, res = 0;
40     for (int k = 1; k <= n; k++)
41     {
42         int tmp = solve(k);
43         if (tmp >= 0 && tmp < minn) { minn = tmp; res = k; }
44     }
45     cout << res << " " << minn << endl;
46     return 0;
47 }