LeetCode #42: Trapping Rain Water - (Precompute)

[WazedKhan]

Summary by CodeRabbit

• New Features

  • Added an algorithm solution for “Trapping Rain Water” with proper handling of edge cases (e.g., empty and single-element inputs).

• Tests

  • Added a parametrized test suite that validates the solution across multiple scenarios (including increasing/decreasing/flat arrays).

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: fcded210-f9b0-4488-b8df-8b23c7f272c5

📥 Commits

Reviewing files that changed from the base of the PR and between 93465da and 032151b.

📒 Files selected for processing (1)

• LeetCode/hard/trap_42.py

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📝 Walkthrough

Walkthrough

Adds a new file LeetCode/hard/trap_42.py implementing Solution.trap for LeetCode problem 42 using a two-pointer algorithm with constant extra space: maintaining left_max and right_max while advancing the pointer on the side with the smaller current maximum. Adds tests/test_leecode_hard.py with parametrized pytest cases covering empty, single-element, monotonic, and flat height inputs.

Changes

Trapping Rain Water two-pointer solution and tests

Layer / File(s)	Summary
Solution.trap two-pointer implementation LeetCode/hard/trap_42.py	Defines Solution class with trap(height: List[int]) -> int, returns 0 for empty input, initializes left and right pointers at endpoints with left_max and right_max from endpoint heights, advances the pointer on the side with the smaller current maximum while updating that side's max and accumulating max - height[pointer] to the result, then returns the total trapped water.
Parametrized pytest coverage tests/test_leecode_hard.py	Introduces test_trap parametrized over multiple input/expected pairs (empty list, single element, increasing, decreasing, flat, and standard examples), asserting Solution().trap(height) matches each expected value.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Poem

🐇 Two pointers dance from outer edges in,
Tracking left and right of tallest win,
Step toward the smaller, fill the gap,
Constant space collects each water drop,
The rabbit's algorithm flows so neat,
Problem 42 is solved—complete! 💧

🚥 Pre-merge checks | ✅ 4 | ❌ 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 (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding a LeetCode solution for problem #42 (Trapping Rain Water) using a two-pointer approach, which aligns with the changeset of adding the solution implementation and corresponding tests.
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.

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✨ 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 leetcode-42

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