Question

The RE in which any number of 0′s is followed by any number of 1′s followed by any number of 2′s is?

(a) (0+1+2)*

(b) 0*1*2*

(c) 0* + 1 + 2

(d) (0+1)*2*

This question was addressed to me by my college professor while I was bunking the class.

The above asked question is from Regular Expression in portion Compiler Introduction of Compiler

Answer 1

Right answer is (b) 0*1*2*

The best explanation: The order for the desired string is 012 and for any number of 0s we write 0* for any number of 1s we denote it by 1* and similarly for 2*.Thus 0*1*2*.