feat(algorithms, heap): trapping rain water ii

[BrianLusina]

Describe your change:

Adds an algorithm to solve for finding how much rain water is trapped in a 3D container(grid) with varying heights per cell.

• 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

• New Features

  • Added support for calculating trapped rainwater across 2D height maps.
  • Added the Trapping Rain Water II problem to the algorithm directory.
  • Updated the directory index with additional algorithm entries.

• Documentation

  • Added problem details, examples, constraints, and related topics for the new algorithm.

• Tests

  • Added coverage for multiple height-map scenarios and expected water totals.

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: df5f144a-68b8-4031-9b98-1911b1380a40

📥 Commits

Reviewing files that changed from the base of the PR and between df8ba80 and 7b1c301.

📒 Files selected for processing (12)

• .github/workflows/directory_writer.yml
• .github/workflows/lint.yml
• .github/workflows/pre-commit.yml
• Makefile
• datastructures/linked_lists/linked_list_utils.py
• datastructures/linked_lists/node.py
• datastructures/linked_lists/singly_linked_list/single_linked_list.py
• datastructures/sparse_vector/test_sparse_vector.py
• datastructures/trees/binary/tree/test_binary_tree_invert_tree.py
• datastructures/trees/heaps/binary/min_heap/min_array_heap.py
• design_patterns/event_stream/processor.py
• pyproject.toml

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 2a9b749b-8fc4-4eee-bb61-06e02c814b0a

📥 Commits

Reviewing files that changed from the base of the PR and between 8a5f81d and df8ba80.

⛔ Files ignored due to path filters (2)

• algorithms/heap/trapping_rain_water_ii/images/examples/trapping_rain_water_ii_example_1.png is excluded by !**/*.png
• algorithms/heap/trapping_rain_water_ii/images/examples/trapping_rain_water_ii_example_2.png is excluded by !**/*.png

📒 Files selected for processing (4)

• DIRECTORY.md
• algorithms/heap/trapping_rain_water_ii/README.md
• algorithms/heap/trapping_rain_water_ii/__init__.py
• algorithms/heap/trapping_rain_water_ii/test_trapping_rain_water_ii.py

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📝 Walkthrough

Walkthrough

The pull request adds Trapping Rain Water II with two min-heap implementations, documentation, and tests. It also updates DIRECTORY.md with links for several algorithm and design-pattern entries.

Changes

Trapping Rain Water II

Layer / File(s)	Summary
Problem contract and heap cell model algorithms/heap/trapping_rain_water_ii/README.md, algorithms/heap/trapping_rain_water_ii/__init__.py	The package documents the problem and adds the public Cell class for height-ordered heap processing.
Boundary traversal and validation algorithms/heap/trapping_rain_water_ii/__init__.py, algorithms/heap/trapping_rain_water_ii/test_trapping_rain_water_ii.py, DIRECTORY.md	trap_rain_water and trap_rain_water_2 process boundary cells and accumulate trapped water. Parameterised tests cover two height maps. The directory index links the new algorithm.

Directory index updates

Layer / File(s)	Summary
Directory catalogue links DIRECTORY.md	The index adds links for Kth Smallest in Lexicographic Order, All O One files, and My Pow.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to df8ba

This PR adds a localized trapping-rain-water algorithm and related documentation and tests; no actionable merge-blocking risk remains beyond normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant trap_rain_water_2
  participant min_heap
  participant height_map
  trap_rain_water_2->>height_map: read boundary cells
  trap_rain_water_2->>min_heap: enqueue boundary Cell objects
  trap_rain_water_2->>min_heap: pop lowest effective height
  trap_rain_water_2->>height_map: inspect unvisited neighbours
  trap_rain_water_2->>min_heap: enqueue neighbours with effective heights

Loading

Poem

I’m a rabbit beside the heap,
Counting water cells in tidy rows.
Boundary heights go in first,
Then trapped blue water grows.
Tests thump softly: all results pass.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description follows the required template, explains the algorithm and documentation changes, and completes the relevant checklist items.
Title check	✅ Passed	The title clearly identifies the new Trapping Rain Water II algorithm and its algorithmic area.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ 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/trap-rain-water-ii

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