feat(algorithms, trie, index pairs): index pairs of strings

[BrianLusina]

Describe your change:

Index Pairs of strings

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

Summary by CodeRabbit

Release Notes

• New Features

  • Added Index Pairs of a String algorithm to the Trie algorithms collection.

• Documentation

  • Added documentation for the Index Pairs of a String algorithm, including examples and complexity analysis.

• Tests

  • Added comprehensive test suite for the Index Pairs of a String algorithm.

[coderabbitai]

📝 Walkthrough

Walkthrough

A new Trie-based algorithm is introduced to find all index pairs of words within a text string. The implementation includes the primary algorithm, comprehensive documentation explaining the approach, and test coverage with multiple fixtures validating the solution.

Changes

Cohort / File(s)	Summary
Documentation Updates DIRECTORY.md, algorithms/trie/index_pairs_of_a_string/README.md	Added directory entry and problem specification document for the new Index Pairs algorithm, detailing constraints, solution approach using Trie traversal, and complexity analysis.
Algorithm Implementation algorithms/trie/index_pairs_of_a_string/__init__.py	Introduced index_pairs() function that constructs a Trie from target words, iterates through text starting positions, traverses the Trie for character matches, and returns sorted index pairs when word matches are detected.
Test Suite algorithms/trie/index_pairs_of_a_string/test_index_pairs_of_a_string.py	Added parameterised unit tests with multiple fixtures validating the index_pairs() function against expected index pair results.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Poem

🐰 A Trie stands tall, with branches so fine,
Index pairs dancing, each one aligned,
Words hide within, now we shall find,
From start to end, no match left behind!
✨ Hop hop, the algorithm's alive! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main change: adding an 'Index Pairs of Strings' algorithm to the Trie data structure section. It is specific, concise, and directly related to the primary objective of the pull request.
Description check	✅ Passed	The description follows the template structure and includes the required sections. However, there are three items marked as completed that appear questionable: 'Fix a bug or typo' and one other checklist item seem misaligned with a PR that primarily adds a new algorithm and documentation.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/algorithms-trie-index-pairs-of-string

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[coderabbitai]

Actionable comments posted: 2

🧹 Nitpick comments (1)

algorithms/trie/index_pairs_of_a_string/__init__.py (1)

13-13: Nit: unused loop variable.

char from enumerate(text) is never read inside the outer loop (the inner loop re-reads via text[j]). Consider for idx in range(len(text)): to make that explicit.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@algorithms/trie/index_pairs_of_a_string/__init__.py` at line 13, The outer
loop currently uses "for idx, char in enumerate(text):" but "char" is never
used; change it to a loop that makes intent explicit (e.g., "for idx in
range(len(text)):" or "for idx, _ in enumerate(text):") in the function that
iterates over the variable text (the outer loop that contains the inner loop
accessing text[j]) so the unused loop variable warning is removed and intent is
clearer.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@algorithms/trie/index_pairs_of_a_string/__init__.py`:
- Around line 4-31: Add a docstring with a concise description of
index_pairs(text, words) inputs and return semantics and include at least one
doctest example; update the index_pairs function (which uses Trie, trie.insert,
trie.root and node.is_end) to have a top-level triple-quoted docstring that
documents parameters and return value and contains a runnable doctest (for
example using text = "thestoryofleetcodeandme", words =
["story","fleet","leetcode"] expecting [[3,7],[9,13]] or another existing
fixture) so automated tests pick it up.

In `@algorithms/trie/index_pairs_of_a_string/README.md`:
- Around line 44-48: Update the "Time Complexity" paragraph to accurately
separate trie construction and search phases: state total complexity as O(n*m +
l*k) (with worst-case search O(l^2)), where n and m refer to the number/average
length of words used to build the trie and l and k refer to the text length and
average/matched word length respectively; explicitly note that l*k describes the
entire search phase across all start indices (not per-index), and keep the
alternative worst-case O(n*m + l^2) to cover degenerate cases.

---

Nitpick comments:
In `@algorithms/trie/index_pairs_of_a_string/__init__.py`:
- Line 13: The outer loop currently uses "for idx, char in enumerate(text):" but
"char" is never used; change it to a loop that makes intent explicit (e.g., "for
idx in range(len(text)):" or "for idx, _ in enumerate(text):") in the function
that iterates over the variable text (the outer loop that contains the inner
loop accessing text[j]) so the unused loop variable warning is removed and
intent is clearer.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 15576026-591f-4789-98ee-b17a74d651f6

📥 Commits

Reviewing files that changed from the base of the PR and between 83eee67 and ee4b9c4.

⛔ Files ignored due to path filters (3)

• algorithms/trie/index_pairs_of_a_string/images/examples/index_pairs_of_a_string_example_1.png is excluded by !**/*.png
• algorithms/trie/index_pairs_of_a_string/images/examples/index_pairs_of_a_string_example_2.png is excluded by !**/*.png
• algorithms/trie/index_pairs_of_a_string/images/examples/index_pairs_of_a_string_example_3.png is excluded by !**/*.png

📒 Files selected for processing (4)

• DIRECTORY.md
• algorithms/trie/index_pairs_of_a_string/README.md
• algorithms/trie/index_pairs_of_a_string/__init__.py
• algorithms/trie/index_pairs_of_a_string/test_index_pairs_of_a_string.py