String matching uses finite automata to effectively search for patterns within text. A finite automaton represents a language as a set of strings and can test if a string matches by running it on the automaton. To perform string matching with a finite automaton, the pattern is represented as states in the automaton. The transition function is computed to define the state transitions for each alphabet symbol. The automaton is run on the text and checks for a transition to the final state to determine if the pattern was found. Real-world applications of finite automata include search engines, text editors, coke machines, and train track switches.

1. STRING MATCHING WITH
FINITE AUTOMATA
Prepared By:
Sabiya Fatima
Email ID: sabiya1990fatima@gmail.com
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2. Contents
1. STRING MATCHING
2. FINITE AUTOMATA
3. FINITE STATE MACHINE
4. STRING MATCHING WITH FINITE AUTOMATA
5. STRING MATCHING AUTOMATA
6. FINITE AUTOMATON MATCHER
7. COMPUTING THE TRANSITION FUNCTION
8. RUNNING TIME
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4. STRING MATCHING:
In General, Whenever you use a search engine, or a
“find” function like grep, you are utilizing a string matching
program. Many of these programs create finite automata in
order to effectively search for your string.
OR
The Objective of string matching is to find the location of
specific text pattern within larger body of text.(a sentence, a
paragraph , a book etc..)
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7. FINITE STATE MACHINE
 A finite state machine (FSM, also known as a
deterministic finite automaton or DFA) is a way of
representing a language.
 we represent the language as the set of those strings
accepted by some program. So, once you've found the
right machine, we can test whether a given string matches
just by running it.
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m+1
|∑|
m
m

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15.  Text: a b a b a b a c a b a
 Pattern: a b a b a c a
size of pattern= 7
No. of alphabet |∑|={a,b,c}
No. of state=7+1 {0 to 7}
Transition Table:
Step1: put the no.s to pattern
Alphabets from1 to 7.
Step2: calculate
no.of(proper prefix=proper suffix)
Ex: aba
Proper prefix=a, ab =1
Proper suffix= ba , a
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State a b c Pattern
0 1 0 0 a
1 2 b
2 3 a
3 4 b
4 5 a
5 6 c
6 7 a
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16. a not proper prefix or suffix so 0
aa =1 ac=0
abb a = b abc a = c
ab = bb ab = bc
And so on
Here abb abc
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State a b c Pattern
0 1 0 0 a
1 1 2 0 b
2 3 0 0 a
3 4 b
4 5 a
5 6 c
6 7 a
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17. Final Transition table
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State a b c Pattern
0 1 0 0 a
1 1 2 0 b
2 3 0 0 a
3 1 4 0 b
4 5 0 0 a
5 1 4 6 c
6 7 0 0 a
7 1 2 0

18. Finite Automata Graph
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60 1 2 53 4 7
a b a b a c a
a
a
a
b
a
b
Text: a b a b a b a c a b a

19. Real life uses of DFA
1. GREP
2. COKE MACHINE
3. THERMOSTATS (FRIDGE)
4. ELEVATORS
5. TRAIN TRACK SWITCHES
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20. Reference
1. REIF, JOHN.
HTTPS://WWW.YOUTUBE.COM/WATCH?V=UH
MFMBPKIH4
2.CORMEN, ET AL. INTRODUCTION TO
ALGORITHMS. ©1990 MIT PRESS, CAMBRIDGE.
862-868.
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Thank You