Regular Expressions 1-29

Question 1

What does λ mean?

Answer 1

Empty String

Question 2

What does + mean?

Answer 2

Or

Question 3

What does * mean?

Answer 3

any number of ( including zero )

Question 4

r = (λ + a)

Answer 4

Either a single a or nothing

Question 5

r = a*

Answer 5

Any number of a’s including no a’s

Question 6

r = (a + b)* (a + bb)

Answer 6

Any string of a’s and b’s ending in either a ‘a’ or ‘bb’

Question 7

r = (aa)* (bb)* b

Answer 7

Any zero or even number of a’s followed by an odd number of b’s

Question 8

Create a regular expression for:
L(r) = {w ∈ {0, 1}* : w has no consecutive zeros}

Answer 8

r = (1 + 01)* (0 + λ)

Question 9

A language that accepts any odd number of b’s

Answer 9

(bb)*b

Question 10

An odd number of a’s followed by a single b

Answer 10

(aa)*ab

Question 11

A string of 0’s and 1’s that contains at least one 0 and one 1

Answer 11

(0+1)(01+10)(0+1)

Question 12

A string of 0’s and 1’s with no consecutive 0’s or 1’s

Answer 12

(0+λ)(10)(1+λ) she said this technically works even though it’s odd

Question 13

(bb)(aa)

Answer 13

An even number of b’s followed by an even number of a’s

Question 14

01*0

Answer 14

0 followed by any number of 1’s followed by another 0

Question 15

ab(ab)

Answer 15

a followed by any number of b’s followed by any number of ab’s