写出奇数个a、偶数个b的正则表达式？

Question

我有一个关于自动机理论和形式语言的问题。写出奇数个a和偶数个b的正则表达式？ 2. Evan a 的个数和 b 的奇数个？

自动机理论中的正则表达式

Answer 1

1 .对于奇数个 a's 和偶数个 b's :

  RE = (aa)*(bb)*a

This regular expression allows the odd number of a's and even number of b's . Ex: aaaabba

2 .对于偶数个 a's 和奇数个 b's :

 We can use the same concept as the above scenario

  RE = (aa)*(bb)*b

This expression allows even number of a's followed by odd number of b's .

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