String Matching Algorithms-The Naive Algorithm

String Matching Algorithms-The Naive Algorithm

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  STRING MATCHING ALGORITHMS A B CA B A A C A B SHIFT=3 A B A A
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  BY: Adeel Rasheed For More Slides and Information Visit:  https://chauhantricks.blogspot.com/
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  WHAT IS STRINGMATCHING • 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.
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  EXAMPLE STRING MATCHING PROBLEM TEXTAB C A B A A C A B SHIFT=3 A B A A
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  Types of SMA The Naive string-matching algorithm  The Rabin-Krap algorithm  String matching with finite automata  The Knuth-Morris-Pratt algorithm
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  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
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  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
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  EXAMPLE SUPPOSE, T=1011101110 P=111 FIND ALL VALIDSHIFT…… 10 1 1 1 0 1 1 1 0 1 1 1P=Patter n T=Text S=0
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  1 0 11 1 0 1 1 1 0 1 1 1 S=1
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  1 0 11 1 0 1 1 1 0 1 1 1 S=2 So, S=2 is a valid shift…
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  1 0 11 1 0 1 1 1 0 S=3 1 1 1
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  1 0 11 1 0 1 1 1 0 S=4 1 1 1
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  1 0 11 1 0 1 1 1 0 1 1 1 S=5
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  1 0 11 1 0 1 1 1 0 S=6 1 1 1 So, S=6 is a valid shift…
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  1 0 11 1 0 1 1 1 0 1 1 1 S=7