Write the Regular expression for the language of all odd length strings defined over ∑ = {a, b}?

Specifying odd length with regular expression

Accepted Strings: 

These all strings are the part of the language so should be accepted by regular expression.

Example strings = {a, b,  aaa, aba, aabba, aabbb,………}and all other strings that contain odd length strings.

Rejected Strings:

These all strings are not part of the language so should be rejected by regular expression.

Example strings = {aa, bb, ab, ba, aaaa, abba, abbb,……………..} and all other strings that do not contain odd length strings.

R.E = (a+b) (aa+bb+ab+ba)^*

Part 1:

Bounding the machine to read only one odd alphabet so the machine can read only a or b.

Part 2:

Bounding the machine to read many times even length alphabet like a machine can read aa or bb or ab or ba and machine can read it many times by repeating the loop(*).

DFA for all odd-length strings

Write the Regular expression for the language of all even length strings but starts with a defined over ∑ = {a, b}?

Accepted Strings: 

These all strings are the part of the language so should be accepted by regular expression.

Example strings = {aa, ab,  aaab, aaab, aabb, abba, ababab………}and all other strings that are started with a and have even length.

Rejected Strings:

These all strings are not part of the language so should be rejected by regular expression.

Example strings = {a, b,  bb, ba, bab, bab, bba, babb,……………..} and all other strings that do not contain odd length strings.

R.E = (ab + aa) (aa+bb+ab+ba)^*

Part 1:

Bounding the machine to read the only even alphabet and starting with a.

Part 2:

Bounding the machine to read many times even length alphabet like a machine can read aa or bb or ab or ba and machine can read it many times by repeating the loop(*).

Deterministic Finite Automata for the language of all even length strings but starts with a

Write the Regular expression for the language of all even length strings but ends with aa defined over ∑ = {a, b}?

Accepted Strings: 

These all strings are part of the language so should be accepted by regular expression.

Example strings = {aa, baaa,  bbaa, babaaa, …….}and all other strings that end with aa and have even length.

Rejected Strings:

These all strings are not part of the language so should be rejected by regular expression.

Example strings = {a, b, ab, ba, bb,  abb, aba, bab, aab, bbab, abbb,……………..} and all other strings that do not contain even length strings and not end with aa.

R.E = (aa+bb+ab+ba)^* aa

Part 1:

Bounding the machine to read many times even length alphabet like the machine can read aa or bb or ab or ba and machine can read it many times by repeating the loop(*).

Part 2:

Bounding the machine to read-only aa at the end. 

List of 100+ Important Regular Expression

Regular expression odd number of 1’s defined over {0,1}.

R.E = 0* (1) (11+0)*

Regular expression odd number of 0’s defined over {0,1}.

R.E = 1* (0) (00+1)*

Regular expression odd number of b’s defined over {a,b}.

R.E = a* (b) (bb+a)*

Regular expression odd number of a’s defined over {a,b}.

R.E = b* (a) (aa+b)*

Regular expression for every odd position is 1 defined over {0,1}

1(01)*

Regular expression for every odd position is 0 defined over {a,b}

0(10)*

Regular expression for every odd position is a defined over {a,b}

a(ba)*

Regular expression for every odd position is b defined over {a,b}

b(ab)*

More Examples of Regular Expression 

• Author
• Recent Posts

Prof. Fazal Rehman Shamil

 CEO @ T4Tutorials.com
I welcome to all of you if you want to discuss about any topic. Researchers, teachers and students are allowed to use the content for non commercial offline purpose. Further, You must use the reference of the website, if you want to use the partial content for research purpose.

Latest posts by Prof. Fazal Rehman Shamil (see all)

• List of Public service commissions - August 31, 2020
• Comparison of fee structure of Pakistani Universities - June 1, 2020
• Past Guess Paper of Auditing - May 12, 2020