Add Trapping Rainwater problem implementation (Two Pointer Approach)

[Arzoo1701]

Description

This PR adds an implementation of the Trapping Rainwater problem using the Two Pointer approach under src/main/java/com/thealgorithms/searches.

Problem Statement

Given an array of non-negative integers representing elevation map heights, compute how much water can be trapped after raining.

Example

Input: [4, 2, 0, 3, 2, 5]
Output: 9

Approach

• Used Two Pointer Technique to achieve O(n) time and O(1) space complexity.
• Added detailed Javadoc comments including reference to the official explanation:
  Wikipedia – Trapping Rain Water

Related Issue

Fixes #6876

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

❌ Patch coverage is 88.88889% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.33%. Comparing base (d28fee9) to head (d0ea66c).

Files with missing lines	Patch %	Lines
...va/com/thealgorithms/stacks/TrappingRainwater.java	88.88%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #6990   +/-   ##
=========================================
  Coverage     78.32%   78.33%           
- Complexity     6655     6660    +5     
=========================================
  Files           751      752    +1     
  Lines         22162    22180   +18     
  Branches       4353     4357    +4     
=========================================
+ Hits          17358    17374   +16     
- Misses         4104     4106    +2     
  Partials        700      700           

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[Arzoo1701]

Hi @alxkm @yanglbme @DenizAltunkapan 👋
All checks have passed for this PR.
Kindly review when you get a chance — thank you! 🙏

[DenizAltunkapan]

@Arzoo1701 Please always add a corresponding test class if you're adding a new algorithm/class. Thank you for your contribution.

[Arzoo1701]

@Arzoo1701 Please always add a corresponding test class if you're adding a new algorithm/class. Thank you for your contribution.

@DenizAltunkapan The requested test class has been added and all checks have passed. Please review and merge when possible. Thank you!

[DenizAltunkapan]

@Arzoo1701 are you sure that both classes should stay in the search package? it seems that this is not a search algorithm

[Arzoo1701]

@DenizAltunkapan
The branch has been updated with the latest main changes.
The Trapping Rain Water algorithm and corresponding test class have been moved to the correct stacks package.
All tests for the Trapping Rain Water algorithm pass .

[DenizAltunkapan]

@Arzoo1701

[DenizAltunkapan]

there is still a changed line in the pom.xml @Arzoo1701