Tutorial 1
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COMPILER CONSTRUCTION
Week 2 Tutorial Questions
Regular Expressions, NFA and DFA
1. Let ∑ = {a,b}. Write regular expressions for the languages over ∑ that contain:
a. All strings.
b. The empty string.
c. The string abb.
d. The strings ba and aba.
e. All strings beginning with ab.
f. All strings beginning with a a and ending with a b.
g. All strings that contain exactly two a’s.
h. All strings in which every a is followed by a b.
2. Construct nondeterministic finite automata (NFA) from the following regular
expressions:
a. (a|b)(a|b)
b. a(a|b)+
c. (ab|b)*a
d. abb(a|b)?a
Note: You may use Thompson’s construction algorithm.
3. Construct deterministic finite automata (DFA) from the NFA’s constructed in
question 2.
4. Minimise the following DFA:
a
B
a
a
a
A
b
a
C
b
b
D
E
b
b
5. Write a phrase using wildcards
to find the following words in a document written in MSWord:
a. Any number.
b. “get” and “got”.
c. Any word that starts with a ‘s’ and ends with ‘t’. E.g. “sit”, “shoot”,…
d. Any word whose beginning is “re”. E.g. “repeat”, “recharge” but not “trend”
