题目：https://www.luogu.com.cn/problem/U242040

设$S \subseteq \{C, O, W\} , s$为字符串

$f_{i,j} = s_i (i = j)$

$f_{i,j} = \complement_S\{s_i,s_j\}(i = j - 1)$

$f_{i,j} = s_j (f_{i,j}= 0)$

$f_{i,j} = 0 (s_j = f_{i,j - 1})$

$f_{i,j}=C$时成立.

时间复杂度$\Theta(n(n - 1))$ 有点高

敢问我的DP对吗，应该如何优化