String matching algorithms are used to find patterns within larger strings or texts. The example shows a text string "A B C A B A A C A B" and a pattern "A B A A" with a shift of 3. The naive string matching algorithm is described which compares characters between the text and pattern from index 0 to the string lengths to find all valid shifts where the pattern occurs in the text.

1. STRING
MATCHING
ALGORITHMS
A B C A B A A C A B
SHIFT=3
A B A A

2. BY: Adeel Rasheed
 For More Slides and Information Visit:
 https://chauhantricks.blogspot.com/

3. WHAT IS STRING MATCHING
• In computer science, string searching
algorithms, sometimes called string
matching algorithms, that try to find a
place where one or several string (also
called pattern) are found within a larger
string or text.

4. EXAMPLE
STRING MATCHING PROBLEM
TEXTA B C A B A A C A B
SHIFT=3
A B A A

5. Types of SMA
 The Naive string-matching algorithm
 The Rabin-Krap algorithm
 String matching with finite automata
 The Knuth-Morris-Pratt algorithm

6. THE NAIVE ALGORITHM
 The idea of the naive solution is just to make a
comparison character by character of the text for all
pattern.
 It returns all the valid shifts found.
 P=Pattern
 T=Text
 S=Shift

7. THE NAIVE ALGORITHM
T[n]=T[0,1…n-1]
P[m]=P[0,1…m-1]
NAIVE-STRING-MATCHER(T,P)
1) n = T.length
2) m = P.length
3) for s=0 to n-m
4) if P[0…m-1]==T[s+0….s+m-1]
5) print” Pattern occurs with shift ” s

8. EXAMPLE
SUPPOSE,
T=1011101110
P=111
FIND ALL VALIDSHIFT……
1 0 1 1 1 0 1 1 1 0
1 1 1P=Patter
n
T=Text
S=0

9. 1 0 1 1 1 0 1 1 1 0
1 1 1
S=1

10. 1 0 1 1 1 0 1 1 1 0
1 1 1
S=2
So, S=2 is a valid shift…

11. 1 0 1 1 1 0 1 1 1 0
S=3
1 1 1

12. 1 0 1 1 1 0 1 1 1 0
S=4
1 1 1

13. 1 0 1 1 1 0 1 1 1 0
1 1 1
S=5

14. 1 0 1 1 1 0 1 1 1 0
S=6
1 1 1
So, S=6 is a valid shift…

15. 1 0 1 1 1 0 1 1 1 0
1 1 1
S=7