Set of operators to use for regular expressions -
c* - zero or more
c+ - one or more
^c - start with a character
c$ - end with a character
a|b - or (multiple conditions)
Use the above operators and create regular expressions
Ex: ^a+b*[c|d]e$ - this expression returns strings starting with a at least once followed by 0 or more occurrence of b and c or d ending with e.