# Regular expression for all strings having 010 or 101

Let us see the Regular expression for all strings having 010 or 101 defined over {0,1}

Regular expression=(0+1)*(010+101)(0+1)*

## DFA for Regular expression of (0+1)*(010+101)(0+1)*

ACCEPTABLE STRINGS (PART OF THIS LANGUAGE)

These strings are part of the given language and must be accepted by our Regular Expression.

• 3 strings of length 1 = no string exist.
• 3 strings of length 2 = no string exist
• 3 strings of length 3 = {101, 010,no more string} .
• 3 strings of length 4 = { 0101, 1011, 0100}.
• 3 strings of length 5 = {10101, 11011, 01010}.
• 3 strings of length 7= {1010110, 1101011, 1101110}.
• 3 strings of length 10 ={0000101011, 1000101001, 1101011011}.
• 3 strings of length 15 = {00001010100001, 011110100010001, 110101101100100}.
• 3 strings of length 20 = {0000101010000111000, 0111010001000100111, 11010110110010011100}.
• 3 string of length 25 ={000010101000011100011011, 011101000100010011100011, 1101011011001001110011010}.
• Many more similar Strings.

Unacceptable strings(not part of this language

These strings are not part of the given language and must be rejected by our Regular Expression.

• 3 strings of length 1={1 ,0, no more string}.
• 3 strings of length 3 = {00,11,10}.
• 3 strings of lenth 5 ={11100,00000,01100}.
• 3 strings of length 7 ={1111000, 1100011, 0000111}.
• 3 strings og length 10 ={1111000111, 1110000111, 0000111100}.
• 3 strings of  length 25={00001111111000011111, 1110000111100001110000000, 00001111110000011110000000}.
• Many more similar Strings.

## Regular expression for all strings having aba or bab

Let us see the Regular expression for all strings having aba or bab defined over {a,b}

# Regular expression=(a+b)*(aba+bab)(a+b)*

ACCEPTABLE STRINGS (PART OF THIS LANGUAGE)

These strings are part of the given language and must be accepted by our Regular Expression.

• 3 strings of length 1 = no string exist.
• 3 strings of length 2 = no string exist
• 3 strings of length 3 = {bab, aba,no more string} .
• 3 strings of length 4 = { abab, babb, abaa}.
• 3 strings of length 5 = {babab, bbabb, ababa}.
• 3 strings of length 7= {bababba, bbababb, bbabbba}.
• 3 strings of length 10 ={aaaabababb, baaababaab, bbababbabb}.
• 3 strings of length 15 = {aaaabababaaaab, abbbbabaaabaaab, bbababbabbaabaa}.
• 3 strings of length 20 = {aaaabababaaaabbbaaa, abbbabaaabaaabaabbb, bbababbabbaabaabbbaa}.
• 3 string of length 25 ={aaaabababaaaabbbaaabbabb, abbbabaaabaaabaabbbaaabb, bbababbabbaabaabbbaabbaba}.
• Many more similar Strings.

Unacceptable strings(not part of this language

These strings are not part of the given language and must be rejected by our Regular Expression.

• 3 strings of length 1={b ,a, no more string}.
• 3 strings of length 3 = {aa,bb,ba}.
• 3 strings of lenth 5 ={bbbaa,aaaaa,abbaa}.
• 3 strings of length 7 ={bbbbaaa, bbaaabb, aaaabbb}.
• 3 strings og length 10 ={bbbbaaabbb, bbbaaaabbb, aaaabbbbaa}.
• 3 strings of  length 25={aaaabbbbbbbaaaabbbbb, bbbaaaabbbbaaaabbbaaaaaaa, aaaabbbbbbaaaaabbbbaaaaaaa}.
• Many more similar Strings.

Regular expression for all strings having 010 or 101

## Tutorial: Regular Expression

A detailed tutorial of the regular expression is here in the link of regular expression tutorial. This page contains the practice questions of regular expressions with solutions.

Tutorial covering the topics

• Give a regular expression.
• Describe the strings of the regular expression.
• write a regular expression.
• create all strings from regular expression.
• Generate all strings from regular expression.
• Extract all strings from regular expression.
• Find all strings from regular expression.
• Examples of regular expression.