Give a regular expression for each of the following languages defined
over alphabet Σ := {0, 1, 2, 3}.
1. {w : The length of w is a multiple of 3} [10 points].
2. {w : w either starts with 01 or ends with 10} [10 points].
3. {w : w does not contain the substring 001} [15 points]. (Only for this part, some justification
and intermediate steps, if any, need to be provided.