正则表达式如何匹配3的倍数？

来自知乎：http://www.zhihu.com/question/24824487/answer/29109747
作者：Belleve

^[0369]* (
  (
    [147][0369]*
  | [258][0369]*[258][0369]*
  ) ([147][0369]*[258][0369]*)* (
    [258][0369]*

  | [147][0369]*[147][0369]*
  )
| [258][0369]*[147][0369]* )* $

得分 488 点，应该还可以优化不过懒得弄了。这个正则是真正正确的，适用于任意十进制数，而不是下面那样作弊的手段。

从下面这个有限自动机逆变得到：

其实，写一个正则匹配 10 进制下 n 的倍数的思路是这样：

• 构造一个有 n 个状态的 DFA，状态为 ，其中起始和接受状态都是 。DFA 中 的含义是「当前读入的数可以被 n 除余 k」。

• 对每个 和 ，计算 ，构造一条 的转移边

这张 DFA 就可以匹配能被 n 整除的十进制数。

下面是被 7 整除的十进制数的正则，长达 12000 余字：

0|(7|[18]5*4|(2|9|[18]5*6)(3|[29]5*6)*(1|8|[29]5*4)|(3|[18]5*[07]|(2|9|[18]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(5|65*4|(0|7|65*6)(3|[29]5*6)*(1|8|[29]5*4))|(4|[18]5*[18]|(2|9|[18]5*6)(3|[29]5*6)*(5|[29]5*[18])|(3|[18]5*[07]|(2|9|[18]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(2|9|35*4|(4|35*6)(3|[29]5*6)*(1|8|[29]5*4)|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(5|65*4|(0|7|65*6)(3|[29]5*6)*(1|8|[29]5*4)))|(5|[18]5*[29]|(2|9|[18]5*6)(3|[29]5*6)*(6|[29]5*[29])|(3|[18]5*[07]|(2|9|[18]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))|(4|[18]5*[18]|(2|9|[18]5*6)(3|[29]5*6)*(5|[29]5*[18])|(3|[18]5*[07]|(2|9|[18]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(0|7|35*[29]|(4|35*6)(3|[29]5*6)*(6|[29]5*[29])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))))(4|[07]5*[29]|(1|8|[07]5*6)(3|[29]5*6)*(6|[29]5*[29])|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))|(3|[07]5*[18]|(1|8|[07]5*6)(3|[29]5*6)*(5|[29]5*[18])|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(0|7|35*[29]|(4|35*6)(3|[29]5*6)*(6|[29]5*[29])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))))*(6|[07]5*4|(1|8|[07]5*6)(3|[29]5*6)*(1|8|[29]5*4)|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(5|65*4|(0|7|65*6)(3|[29]5*6)*(1|8|[29]5*4))|(3|[07]5*[18]|(1|8|[07]5*6)(3|[29]5*6)*(5|[29]5*[18])|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(2|9|35*4|(4|35*6)(3|[29]5*6)*(1|8|[29]5*4)|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(5|65*4|(0|7|65*6)(3|[29]5*6)*(1|8|[29]5*4))))|(6|[18]5*3|(2|9|[18]5*6)(3|[29]5*6)*(0|7|[29]5*3)|(3|[18]5*[07]|(2|9|[18]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(4|65*3|(0|7|65*6)(3|[29]5*6)*(0|7|[29]5*3))|(4|[18]5*[18]|(2|9|[18]5*6)(3|[29]5*6)*(5|[29]5*[18])|(3|[18]5*[07]|(2|9|[18]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(1|8|35*3|(4|35*6)(3|[29]5*6)*(0|7|[29]5*3)|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(4|65*3|(0|7|65*6)(3|[29]5*6)*(0|7|[29]5*3)))|(5|[18]5*[29]|(2|9|[18]5*6)(3|[29]5*6)*(6|[29]5*[29])|(3|[18]5*[07]|(2|9|[18]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))|(4|[18]5*[18]|(2|9|[18]5*6)(3|[29]5*6)*(5|[29]5*[18])|(3|[18]5*[07]|(2|9|[18]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(0|7|35*[29]|(4|35*6)(3|[29]5*6)*(6|[29]5*[29])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))))(4|[07]5*[29]|(1|8|[07]5*6)(3|[29]5*6)*(6|[29]5*[29])|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))|(3|[07]5*[18]|(1|8|[07]5*6)(3|[29]5*6)*(5|[29]5*[18])|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(0|7|35*[29]|(4|35*6)(3|[29]5*6)*(6|[29]5*[29])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))))*(5|[07]5*3|(1|8|[07]5*6)(3|[29]5*6)*(0|7|[29]5*3)|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(4|65*3|(0|7|65*6)(3|[29]5*6)*(0|7|[29]5*3))|(3|[07]5*[18]|(1|8|[07]5*6)(3|[29]5*6)*(5|[29]5*[18])|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(1|8|35*3|(4|35*6)(3|[29]5*6)*(0|7|[29]5*3)|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(4|65*3|(0|7|65*6)(3|[29]5*6)*(0|7|[29]5*3)))))(2|9|45*3|(5|45*6)(3|[29]5*6)*(0|7|[29]5*3)|(6|45*[07]|(5|45*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(4|65*3|(0|7|65*6)(3|[29]5*6)*(0|7|[29]5*3))|(0|7|45*[18]|(5|45*6)(3|[29]5*6)*(5|[29]5*[18])|(6|45*[07]|(5|45*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(1|8|35*3|(4|35*6)(3|[29]5*6)*(0|7|[29]5*3)|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(4|65*3|(0|7|65*6)(3|[29]5*6)*(0|7|[29]5*3)))|(1|8|45*[29]|(5|45*6)(3|[29]5*6)*(6|[29]5*[29])|(6|45*[07]|(5|45*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))|(0|7|45*[18]|(5|45*6)(3|[29]5*6)*(5|[29]5*[18])|(6|45*[07]|(5|45*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(0|7|35*[29]|(4|35*6)(3|[29]5*6)*(6|[29]5*[29])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))))(4|[07]5*[29]|(1|8|[07]5*6)(3|[29]5*6)*(6|[29]5*[29])|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))|(3|[07]5*[18]|(1|8|[07]5*6)(3|[29]5*6)*(5|[29]5*[18])|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(0|7|35*[29]|(4|35*6)(3|[29]5*6)*(6|[29]5*[29])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))))*(5|[07]5*3|(1|8|[07]5*6)(3|[29]5*6)*(0|7|[29]5*3)|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(4|65*3|(0|7|65*6)(3|[29]5*6)*(0|7|[29]5*3))|(3|[07]5*[18]|(1|8|[07]5*6)(3|[29]5*6)*(5|[29]5*[18])|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(1|8|35*3|(4|35*6)(3|[29]5*6)*(0|7|[29]5*3)|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(4|65*3|(0|7|65*6)(3|[29]5*6)*(0|7|[29]5*3)))))*(3|45*4|(5|45*6)(3|[29]5*6)*(1|8|[29]5*4)|(6|45*[07]|(5|45*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(5|65*4|(0|7|65*6)(3|[29]5*6)*(1|8|[29]5*4))|(0|7|45*[18]|(5|45*6)(3|[29]5*6)*(5|[29]5*[18])|(6|45*[07]|(5|45*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(2|9|35*4|(4|35*6)(3|[29]5*6)*(1|8|[29]5*4)|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(5|65*4|(0|7|65*6)(3|[29]5*6)*(1|8|[29]5*4)))|(1|8|45*[29]|(5|45*6)(3|[29]5*6)*(6|[29]5*[29])|(6|45*[07]|(5|45*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))|(0|7|45*[18]|(5|45*6)(3|[29]5*6)*(5|[29]5*[18])|(6|45*[07]|(5|45*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(0|7|35*[29]|(4|35*6)(3|[29]5*6)*(6|[29]5*[29])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))))(4|[07]5*[29]|(1|8|[07]5*6)(3|[29]5*6)*(6|[29]5*[29])|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))|(3|[07]5*[18]|(1|8|[07]5*6)(3|[29]5*6)*(5|[29]5*[18])|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(0|7|35*[29]|(4|35*6)(3|[29]5*6)*(6|[29]5*[29])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(3|65*[29]|(0|7|65*6)(3|[29]5*6)*(6|[29]5*[29]))))*(6|[07]5*4|(1|8|[07]5*6)(3|[29]5*6)*(1|8|[29]5*4)|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(5|65*4|(0|7|65*6)(3|[29]5*6)*(1|8|[29]5*4))|(3|[07]5*[18]|(1|8|[07]5*6)(3|[29]5*6)*(5|[29]5*[18])|(2|[07]5*[07]|(1|8|[07]5*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))(6|35*[18]|(4|35*6)(3|[29]5*6)*(5|[29]5*[18])|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(2|9|65*[18]|(0|7|65*6)(3|[29]5*6)*(5|[29]5*[18])))*(2|9|35*4|(4|35*6)(3|[29]5*6)*(1|8|[29]5*4)|(5|35*[07]|(4|35*6)(3|[29]5*6)*(4|[29]5*[07]))(1|8|65*[07]|(0|7|65*6)(3|[29]5*6)*(4|[29]5*[07]))*(5|65*4|(0|7|65*6)(3|[29]5*6)*(1|8|[29]5*4))))))*

下面教你怎么把 DFA 转正则：

还是从它开始

我们记 A 为终止到状态 A 的字符串集合，BC 类似，那么可以列出三个方程：

A = A[0369] | B[258] | C[147] |
B = A[147] | B[0369] | C[258]
C = A[258] | B[147] | C[0369]

根据正则语言的特性，可以推导出如下形式的方程

L = LU|V

有解

L = VU*

因此上面方程可以修改为

A = (| B[258] | C[147])[0369]* (1)
B = (A[147] | C[258])[0369]* (2)
C = (A[258] | B[147])[0369]* (3)

将 (3) 代入 (1) (2) 得

A = (| B[258] | (A[258] | B[147])[0369]*[147])[0369]* (4)
B = (A[147] | (A[258] | B[147])[0369]*[258])[0369]* (5)

用分配律展开 (5) 中的竖线得到

B = A[147][0369]* | A[258][0369]*[258][0369]* | B[147][0369]*[258][0369]*

故

B = A[147][0369]*([147][0369]*[258][0369]*)* 
  | A[258][0369]*[258][0369]*([147][0369]*[258][0369]*)*

把它代入 (4) 得

A = (| B[258] | (A[258] | B[147])[0369]*[147])[0369]*
  =   [0369]* 
    | B[258][0369]*
    | A[258][0369]*[147][0369]*
    | B[147][0369]*[147][0369]* 
  =   [0369]* 
    | A[147][0369]*([147][0369]*[258][0369]*)*[258][0369]*
    | A[258][0369]*[258][0369]*([147][0369]*[258][0369]*)*[258][0369]*
    | A[258][0369]*[147][0369]*
    | A[147][0369]*([147][0369]*[258][0369]*)*[147][0369]*[147][0369]* 
    | A[258][0369]*[258][0369]*([147][0369]*[258][0369]*)*[147][0369]*[147][0369]* 
  = [0369]* (
                  [147][0369]*([147][0369]*[258][0369]*)*[258][0369]*
    | [258][0369]*[258][0369]*([147][0369]*[258][0369]*)*[258][0369]*
    |             [147][0369]*([147][0369]*[258][0369]*)*[147][0369]*[147][0369]* 
    | [258][0369]*[258][0369]*([147][0369]*[258][0369]*)*[147][0369]*[147][0369]*
    | [258][0369]*[147][0369]* )*
  = [0369]* (
      (
        [147][0369]*
      | [258][0369]*[258][0369]*
      ) ([147][0369]*[258][0369]*)* (
        [258][0369]*

      | [147][0369]*[147][0369]*
      )
    | [258][0369]*[147][0369]* )*

加上 ^ 和 $ 就行了，放去测试，全部正确。

（编辑：李大同）

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