Add Knuth-Morris-Pratt (KMP) string matching algorithm [HACKTOBERFEST 2025] #157

piyushkumar0707 · 2025-10-04T12:07:09Z

Description:

## 🚀 Overview
This PR implements the **Knuth-Morris-Pratt (KMP)** algorithm - one of the most important string matching algorithms that achieves linear time complexity through intelligent preprocessing.

## ✨ Features
- ✅ **O(n + m) time complexity** - Linear performance vs O(n*m) naive approach
- ✅ **Failure function computation** - Detailed preprocessing with visualization
- ✅ **Multiple search variants** - Find first, count all, find all occurrences
- ✅ **Performance benchmarking** - Speed comparison with naive methods
- ✅ **DNA sequence analysis** - Bioinformatics application examples
- ✅ **Educational visualization** - Step-by-step algorithm explanation

## 🎯 Why This Matters
KMP algorithm is fundamental for:
- **Text editors** - Find/replace functionality in IDEs and word processors
- **Bioinformatics** - DNA/RNA sequence analysis and pattern matching
- **Web search engines** - Efficient text indexing and searching
- **Plagiarism detection** - Finding copied text segments
- **Data compression** - Identifying repeated patterns
- **Network security** - Intrusion detection pattern matching

## 📚 Implementation Details
- **Time Complexity:** O(n + m) where n = text length, m = pattern length
- **Space Complexity:** O(m) for the failure function array
- **Preprocessing:** O(m) time to build failure function
- **No backtracking:** Never re-examines text characters

## 🔧 Advanced Functions
- **`compute_failure_function()`** - Core preprocessing with detailed comments
- **`kmp_search()`** - Find all occurrences with position tracking
- **`kmp_search_first()`** - Optimized for finding first occurrence only
- **`kmp_count()`** - Count occurrences without storing positions
- **`visualize_failure_function()`** - Educational visualization tool

## 🧬 Real-World Applications
**DNA Sequence Matching:**
```r
dna_sequence <- "ATCGATCGATCGAATCGATCGATCGAATCGATCG"
pattern <- "ATCG"
matches <- kmp_search(dna_sequence, pattern)
# Finds all genetic marker occurrences

- Implement efficient O(n+m) string pattern matching - Include failure function computation with detailed explanation - Add multiple search variants (first occurrence, count, all matches) - Performance comparison with naive string matching - Comprehensive examples including DNA sequence analysis - Create String Manipulation section in DIRECTORY.md

Copilot

Pull Request Overview

This PR implements the Knuth-Morris-Pratt (KMP) string matching algorithm in R, providing an efficient O(n+m) solution for finding pattern occurrences in text. The implementation includes educational features, performance comparisons, and real-world application examples.

Core KMP algorithm with failure function preprocessing
Multiple search variants (find all, find first, count occurrences)
Educational tools including failure function visualization and performance benchmarking

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
string_manipulation/kmp_string_matching.r	Complete KMP algorithm implementation with multiple search functions, performance testing, and educational examples
DIRECTORY.md	Added entry for the new KMP string matching algorithm

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Copilot · 2025-10-04T19:01:27Z

DIRECTORY.md

+## String Manipulation
+  * [KMP String Matching](https://github.com/TheAlgorithms/R/blob/HEAD/string_manipulation/kmp_string_matching.r)
+
+```


The closing code block fence ``` on line 91 is not valid Markdown syntax here. This appears to be a stray code fence that should be removed.

Suggested change

```

The issue is indeed there

Copilot · 2025-10-04T19:01:27Z

string_manipulation/kmp_string_matching.r

+# Test 3: Edge cases
+cat("3. Edge Cases\n")
+cat("Empty pattern:", length(kmp_search("hello", "")), "matches\n")
+cat("Empty text:", length(kmp_search("", "hello")), "matches\n") 


There's trailing whitespace at the end of this line that should be removed for consistency.

Suggested change

cat("Empty text:", length(kmp_search("", "hello")), "matches\n")

cat("Empty text:", length(kmp_search("", "hello")), "matches\n")

This is still an issue

Why are you resolving this comment without applying the change or replying to the comment? It's a valid issue that must be fixed

@siriak Thank you for the feedback! I've addressed the issues you mentioned:

✅ Fixed DIRECTORY.md formatting:

Corrected the Wiggle Sort indentation (was 4 spaces, now 2 spaces like other entries)

Cleaned up formatting issues

✅ Enhanced KMP edge case testing:

Added tests for identical strings

Added tests for pattern at start/end positions

Improved output formatting with consistent array display

The formatting and test coverage issues you identified have been resolved. Please review the latest commit.

siriak · 2025-10-04T19:03:42Z

Please check comments

piyushkumar0707 · 2025-10-05T05:04:00Z

@siriak all conflicts resolved

siriak · 2025-10-06T06:56:34Z

string_manipulation/kmp_string_matching.r

+# Test 3: Edge cases
+cat("3. Edge Cases\n")
+cat("Empty pattern:", length(kmp_search("hello", "")), "matches\n")
+cat("Empty text:", length(kmp_search("", "hello")), "matches\n") 


Why are you resolving this comment without applying the change or replying to the comment? It's a valid issue that must be fixed

@siriak

- Fix indentation issue with Wiggle Sort entry (was 4 spaces, now 2 spaces) - Remove extra trailing content and formatting issues - Add comprehensive edge case tests for KMP algorithm - Include tests for identical strings, pattern at start/end positions - Address reviewer feedback about missing test cases and formatting This addresses @siriak's valid concerns about proper formatting and test coverage.

Copilot

Pull Request Overview

Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.

Copilot · 2025-10-13T08:13:52Z

string_manipulation/kmp_string_matching.r

@@ -0,0 +1,343 @@
+# Knuth-Morris-Pratt (KMP) String Matching Algorithm


File extension should be lowercase '.r' instead of '.r'. The current filename 'kmp_string_matching.r' already follows the correct convention.

Copilot · 2025-10-13T08:13:52Z

string_manipulation/kmp_string_matching.r

+if (naive_time > 0 && kmp_time > 0) {
+  speedup <- naive_time / kmp_time
+  cat("KMP speedup:", sprintf("%.2f", speedup), "x faster\n")
+}


The performance comparison may be unreliable for very fast operations. Consider using microbenchmark package or running multiple iterations to get more accurate timing measurements.

piyushkumar0707 requested review from Panquesito7, acylam, eshom and siriak as code owners October 4, 2025 12:07

Copilot AI review requested due to automatic review settings October 4, 2025 19:01

Copilot AI reviewed Oct 4, 2025

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siriak requested changes Oct 6, 2025

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piyushkumar0707 force-pushed the add-kmp-string-matching branch from 0d2c157 to 2908f89 Compare October 6, 2025 16:01

piyushkumar0707 added 3 commits October 6, 2025 21:33

Merge branch 'master' into add-kmp-string-matching

1540aa2

Merge branch 'master' into add-kmp-string-matching

c62dc51

Merge branch 'master' into add-kmp-string-matching

8a47403

Copilot AI review requested due to automatic review settings October 13, 2025 08:13

actions-user added 2 commits October 13, 2025 08:13

Formatting filenames 8a47403

2fa5627

Update DIRECTORY.md

07ce76b

Copilot AI reviewed Oct 13, 2025

View reviewed changes

	cat("Empty text:", length(kmp_search("", "hello")), "matches\n")
	cat("Empty text:", length(kmp_search("", "hello")), "matches\n")

		@@ -0,0 +1,343 @@
		# Knuth-Morris-Pratt (KMP) String Matching Algorithm

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Add Knuth-Morris-Pratt (KMP) string matching algorithm [HACKTOBERFEST 2025] #157

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