🚀 Added 4 Optimized Sliding Window Problems in C++ (max sum, unique substring, anagrams, min window)

[kinngddx]

Have you read the Contributing Guidelines on Pull Requests?

Yes ✅

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Description

This PR adds a new C-Plus-Plus/slidingwindow/ folder containing 4 optimized Sliding Window algorithm problems in C++.
Each program is well-commented, beginner-friendly, and follows the NeoAlgo contribution format.

Files added:

1. max_sum_subarray.cpp — Maximum sum of subarray of size K
2. longest_substring_no_repeat.cpp — Longest substring without repeating characters
3. count_anagrams.cpp — Count occurrences of anagrams in a string
4. min_window_substring.cpp — Minimum window substring

Also added:

• README.md → explains all problems, complexities, and how to run the files.

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Checklist

• I've read the contribution guidelines.
• I've checked the issue list before deciding what to submit.
• I've added my code in the correct folder (C-Plus-Plus/slidingwindow/).
• I've edited the README.md and linked my code.
• My code is well-commented and runs without errors.
• I’ve ensured no plagiarism — all solutions are original.

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Related Issues or Pull Requests

Fixes #<issue_number_if_any>
(If this PR is not linked to an issue, you can leave this blank or write “New addition — no issue created”)

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💡 Additional Notes

All problems are implemented using efficient O(n) Sliding Window techniques with hash maps and two-pointer optimization.
This PR enhances C++ coverage of important pattern-based algorithms for Hacktoberfest 2025 🎃