CPP/strings: Add shift_cipher solution (shift cipher problem)

[Mojirade18]

What I added

• Language: C++
• File: CPP/strings/shift_cipher.cpp

Problem

Short description: Shift letters forward/backward by k depending on whether "the" appears as a separate word.

Approach

• Iterate over the string, shift alphabetic characters with wrap-around.
• Check for "the" as a word using case-insensitive check.

Time/Space Complexity

• Time: O(L) per test case (L = length of input string)
• Space: O(L) for output string

Tests performed

• compiled with g++
• sample tests run: [list sample inputs/outputs]
• edge cases: uppercase letters, punctuation, multiple spaces

Thank you! Feedback welcome.

[github-actions]

🎉 Welcome to Hacktoberfest 2025, @Mojirade18! 🎃

Thank you for your first contribution to our DSA repository! Here's what happens next:

🔍 Automatic Checks

• ✅ Code Validation: Passed
• 🧪 Compilation Tests: Passed

📋 Next Steps

🎯 Great job! Your code compiled successfully. Maintainers @admirerr and @kartikey2991 will review your PR soon.

🎁 What You Get

• 🏆 Hacktoberfest Credit: This PR counts toward your 6 PR goal for exclusive T-shirt + Tree!
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💡 Tips for Success

• Follow our Contributing Guidelines
• Add comments explaining your algorithm
• Include time/space complexity analysis
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Welcome to the community! 🚀

[github-actions]

🤖 Automated PR Status

🔍 Code Validation

✅ Passed - File naming and structure look good!

🧪 Compilation Tests

✅ Passed - All code compiles successfully!

📋 Overall Status

🎉 Ready for Review - Your PR has passed all automated checks!
👥 Maintainers have been notified for review.

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[admirerr]

Approved

[Mojirade18]

hacktoberfest said this repo has been excluded and my pr wont count. can i know why