Add Count Segments String Algorithm in R

[Siddhram]

This PR introduces a comprehensive and well-documented implementation of the Count Segments problem in R for efficient word boundary detection and segment counting.

Overview

The algorithm counts the number of segments (words) in a given string by detecting word boundaries.
A segment is defined as a sequence of non-space characters, and segments are separated by one or more spaces.
It efficiently identifies transitions from space to non-space characters to determine segment counts.

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Features

• Optimized O(n) boundary detection algorithm
  • Iterates through each character once
  • Increments count when current != ' ' AND (i == 1 OR previous == ' ')
• Handles leading, trailing, and multiple consecutive spaces correctly
• Multiple implementation variants:
  • count_segments() – Primary boundary detection method
  • count_segments_regex() – Regex-based alternative for validation
  • count_segments_vectorized() – Vectorized version for multiple string inputs
• Robust input validation and error handling
• Comprehensive test suite with edge cases
• Consistent roxygen2 documentation and code structure with other string_manipulation scripts

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Complexity

• Time Complexity: O(n) — Each character is processed exactly once
• Space Complexity: O(1) — Constant space (or O(n) due to R’s internal character vector representation)

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Directory

• Updated DIRECTORY.md
  Added: "Count Segments" entry under String Manipulation

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Demonstration

Run the following script to execute built-in examples and test cases:

PowerShell

Rscript "string_manipulation/count_segments.r"