Categories of Regular Expressions

 

Category 1: Basic Regular Expressions

Sr.	Regular Expression	Explanation
1	a	Only a single character "a".
2	ab	Sequence "a" followed by "b".
3	(a+b)	Either "a" or "b".
4	(a)*	Zero (ε) or more occurrences of "a".
5	(ab)*	Zero (ε) or more repetitions of the sequence “ab".
6	(a+b)*	Zero (ε) or more symbols from the alphabet {a,b} of any length, any order.
7	(a)+	One or more occurrences of "a".
8	(ab)+	One or more repetitions of the sequence "ab".
9	(a+b)+	One or more symbols chosen from "a" or "b".
10	(10+1)*	Zero (ε) or more repetitions of "10" or "1".
11	(01+10+1)*	Zero (ε) or more repetitions of "01", "10", or "1".
12	(a+b+c+d)*	Zero (ε) or more symbols chosen from "a", "b", "c", or "d".
13	(a+b+c+d)+	One or more symbols chosen from "a", "b", "c", or "d".
14	(ab+bb+cc+dd)*	Zero (ε) or more repetitions of "ab", "bb", "cc", or "dd".
15	101 + (0+1)*1	Either "101" or any combination of 0s and "1s” ending in "1".
16	11 + 00 + 0 + 10*	Either "11", "00", a single "0", or "1" followed by zero or more "0s”.
17	1(0 + 11) + 0(00 + 1)	Either "1" followed by "0" or "11", or "0" followed by "00" or "1".
18	ba + (aa + b)*	Either "ba" or any number of repetitions of "aa" or "b".
19	aa + ba + (aa + b)*	Either "aa", "ba", or any number of repetitions of "aa" or "b".
20	(00)*(0 + 1) + (1)*	Zero (ε) or more "00"s followed by 0 or 1, or any number of "1s”.
21	(001)* + (00)	Zero (ε) or more repetitions of "001", or exactly "00".

Category 2: Start with Regular Expressions

r.	Regular Expression	Simple Explanation
1	a(a+b)*	Starts with a, followed by any number (even zero) of as or bs in any order.
2	101*(0+1)*	Starts with 10, then zero or more repeats of 1, then zero or more mix of 0s and 1s.
3	bab(a+b)*	Starts with bab, followed by zero or any number of as or bs .
4	aa(aba+bab)*	Starts with aa, followed by zero or any number of the patterns aba or bab.
5	(a(bb)*)(a+b)*	Starts with a, then zero or more bbs, then zero or any number of as or bs in any order.
6	1(0+1)(00+11)*	Starts with 1, then either 0 or 1, then zero or more repeats of 00 or 11.
7	a+b+c(ab+bb+cc)*	One"a", One “b”, or starts with"cand then zero or more repeats of ab, bb, or cc patterns.
8	a+b+c+d(ab+bb+cc+dd)*	One"a", One “b”, One “c” or starts with"dand then zero or more repeats of ab, bb, cc, or dd patterns.
9	aba(a+b)* + bab(a+b)*	Either starts with aba or bab, followed by zero or any number of as or bs

Category 3: End with Regular Expressions

Sr.	Regular Expression	Simple Explanation
1	(a+b+c+d)*ab	Any mix of a, b, c, d (including empty), ending with ab.
2	(aaa+bbb)*ba	Repeats of aaa or bbb (or none), ending with ba.
3	(a+b+c)*abc	Any mix of a, b, or c (including empty), ending with abc.
4	(0+1)*101*	Any mix of 0s and 1s, followed by 10, and then any number of 1’s.
5	(a+b)*a(a+b)b	Any mix of a and b, then an aa or ab,and ending with b.
6	(00+11)*1(0+1)	Repeats of 00 or 11 (or none), followed by 1, and then either 0 or 1

Category 4: Start and End with Regular Expressions

Sr.	Regular Expression	Simple Explanation
1	1(1+0)*1 + 0(1+0)*0	Strings that start and end with 1 or start and end with 0, and mix of 0, 1 in between
2	11(0+1)(00)	Starts with 11, then either 0 or 1, and ends with 00.
3	00(11)*101	Starts with 00, followed by any number of 11's, and ends with 101.
4	aba(aa+b)*ba	Starts with aba, followed by any number of aa or b, and ends with ba.
5	b*(aaa+bbb)*ba	Any number of bs, followed by any number of aaa or bbb, and ending with ba.
6	a(a+b)*ba + a	Either just a, or starts with a, followed by any mix of as and bs, and ends with ba.
7	0 + 1(0+1)*10	Either a single 0, or a string starting with 1, then anything over 0,1, and ending with 10.
8	(11)*(0+1)(00)	Repeats of 11, followed by either 0 or 1, and ending with 00.
9	(1)*(0+1)*(00)*	Any number of 1s, followed by any combination of 0s and 1s, followed by any number of 00s.
10	10(101+0+1)*1	Starts with 10, followed by any number of 101, 0, or 1, and ends with 1.
11	ac(a+b+c)*ba	Starts with ac, then any mix of a, b, or c, and ends with ba.
12	d(a+b+c)*bad	Starts with d, then any mix of a, b, or c, and ends with bad.
13	acd(a+b+c)*bad	Starts with acd, then any mix of a, b, or c, and ends with bad.
14	bb(a+b)*aa(aa+bb)	Starts with bb, followed by any mix of as and bs, then aa, and ends with either aa or bb.
15	(aa+bb)((aa)*+b)*ba	Starts with aa or bb, followed by any number of aas or bs, and ends with ba.