Pattern Searching

Pattern searching algorithms are essential tools in computer science and data processing. These algorithms are designed to efficiently find a particular pattern within a larger set of data. Pattern searching algorithms play important role in tasks such as text processing, data mining, and information retrieval.

Patten Searching

What is Pattern Searching?

Pattern searching is a fundamental operation in data structures and algorithms. It involves finding a specific pattern or substring within a given text or string. Efficient pattern searching algorithms are essential for various applications, including text processing, information retrieval, and bioinformatics.

Important Pattern Searching Algorithms:

1. Naive String Matching

The naive string matching algorithm is the simplest pattern searching algorithm. It compares the pattern with every possible substring of the text. The time complexity of this algorithm is O(mn), where m is the length of the pattern and n is the length of the text.

2. Knuth-Morris-Pratt (KMP) Algorithm

The KMP algorithm is a heuristic algorithm that uses a precomputed failure function to skip unnecessary comparisons. The failure function indicates the length of the longest proper prefix of the pattern that is also a suffix of the current substring. The time complexity of the KMP algorithm is O(m + n), where m is the length of the pattern and n is the length of the text.

3. Rabin-Karp Algorithm

The Rabin-Karp algorithm is a heuristic algorithm that uses hashing to compare the pattern with the text. It computes a hash value for the pattern and for each substring of the text. If the hash values match, it performs a character-by-character comparison to confirm the match. The time complexity of the Rabin-Karp algorithm is O(m + n), where m is the length of the pattern and n is the length of the text.

4. Aho-Corasick Algorithm

The Aho-Corasick algorithm is a deterministic finite automaton (DFA) based algorithm that is used for multiple pattern searching. It constructs a DFA from a set of patterns and then uses the DFA to find all occurrences of the patterns in the text. The time complexity of the Aho-Corasick algorithm is O(m + n), where m is the total length of all patterns and n is the length of the text.

Applications of Pattern Searching

Pattern searching algorithms have numerous applications, including:

• Text Processing: Searching for keywords in a document, finding and replacing text, spell checking, and plagiarism detection.
• Information Retrieval: Finding relevant documents in a database, web search, and data mining.
• Bioinformatics: Searching for DNA sequences in a genome, protein analysis, and gene expression analysis.
• Network Security: Detecting malicious patterns in network traffic, intrusion detection, and malware analysis.
• Data Mining: Identifying patterns in large datasets, customer segmentation, and fraud detection.

Learn Basics of Pattern Searching:

• Introduction to Pattern Searching – Data Structure and Algorithm Tutorial
• Naive Pattern Searching

Standard Pattern Searching Algorithms:

• Rabin-Karp Algorithm
• KMP Algorithm
• Z algorithm (Linear time pattern searching Algorithm)
• Finite Automata
• Boyer Moore Algorithm – Bad Character Heuristic
• Aho-Corasick Algorithm for Pattern Searching
• Suffix Array
• kasai’s Algorithm for Construction of LCP array from Suffix Array
• Online algorithm for checking palindrome in a stream
• Manacher’s Algorithm – Linear Time Longest Palindromic Substring – Part 4
• Ukkonen’s Suffix Tree Construction – Part 1
• Generalized Suffix Tree

Practice Problems on Pattern Searching:

• Pattern Searching using C++ library
• Anagram Substring Search (Or Search for all permutations)
• Pattern Searching using a Trie of all Suffixes
• Dynamic Programming | Wildcard Pattern Matching | Linear Time and Constant Space
• Longest prefix which is also suffix
• Count of number of given string in 2D character array
• Find all the patterns of “1(0+)1” in a given string (General Approach)
• Maximum length prefix of one string that occurs as subsequence in another
• Wildcard Pattern Matching
• Search a Word in a 2D Grid of characters
• String matching where one string contains wildcard characters
• Suffix Tree Application 1 – Substring Check

Quick Links:

• Learn Data Structure and Algorithms | DSA Tutorial
• Practice problems on Pattern Searching

Recommended:

• Learn Data Structure and Algorithms | DSA Tutorial