Write a regular expression for each of the following languages: (a) Given an alp

Question

Write a regular expression for each of the following languages:

(a) Given an alphabet = {0, 1}, L is the set of all strings of alternating pairs of 0s and pairs of 1s.

(b) Given an alphabet = {0, 1}, L is the set of all strings of 0s and 1s that contain an even number of 0s or an even number of 1s.

(c) Given an alphabet = {a, b, c, d}, L is the set of all strings in which the letters appear in strictly ascending lexicographical order. Strictly ascending means that the same letter can’t appear twice.

Explanation / Answer

a
(0011)*(00)? | (1100)*(11)?

b
   (((10|01)(00|11)*(10|01))|(00|11))*

c
   (a?b?c?d?)
OR
    (ab?c?d?)(a?bc?d?)(a?b?cd?)(a?b?c?d)

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