🚀 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 ✅

---

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.

---

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.

---

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”)

---

💡 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 🎃

[github-actions]

Please reopen this pull request once you commit the changes requested or make improvements on the code. If this is not the case and you need some help, feel free to seek help from our Discord or ping one of the reviewers. Thank you for your contributions!