Question

Write regular expression to denote a language L
a) String which begin or end with either 00 or 11.
b) The set of all strings, when viewed as binary representation of integers, that are divisible by 2.
c) The set of all strings containing 00.
d) String not containing the substring 110.

Answer 1

1.    (00+11) (0+1)* + ( 0 + 1)* (00+11)
2.    ( 0 + 1)*0      i.e all strings ending with 0
3.    (0+1)*00 (0+1)*
4.    (0+10) *1*