Program to construct DFA for Regular Expression C( A + B)+

Given a string S, the task is to design a Deterministic Finite Automata (DFA) for accepting the language L = C (A + B)+. If the given string is accepted by DFA, then print "Yes". Otherwise, print "No".

Examples:

Input: S = "CABABABAB"
Output: Yes
Explanation: The given string is of the form C(A + B)+ as the first character is C and it is followed by A or B.

Input: S = "ABAB"
Output: No

Approach: The idea is to interpret the given language L = C (A + B)+ and for the regular expression of the form C(A + B)+, the following is the DFA State Transition Diagram:

Follow the steps below to solve the problem:

• If the given string is of length less than equal to 1, then print "No".
• If the first character is always C, then traverse the remaining string and check if any of the characters is A or B.
• If there exists any character other than A or B while traversing in the above step, then print "No".
• Otherwise, print "Yes".

Below is the implementation of the above approach:

Yes

Time Complexity: O(N)
Auxiliary Space: O(1)