Fix: prevent out-of-bounds write in counting sort for strings

[Khush0031]

Fix : #3055

Description of Change

This fixes an out-of-bounds access in the string counting sort implementation located at sorting/counting_sort_string.cpp. The previous implementation wrote into an empty std::string (output) without pre-allocating it, which causes undefined behavior and potential crashes.

Changes

• countSort now takes std::string& (modify in-place).
• output is pre-allocated to the input length.
• Uses unsigned char when indexing the count array to avoid negative/undefined indexing.
• Builds output with right-to-left iteration to preserve stability.
• Early return for empty or single-character strings.

Testing

• Basic test program included (locally) was used to verify expected sorted outputs for several strings including edge cases (empty string, single char).

Checklist

• Added description of change
• Added file name matches File name guidelines
• Added tests and example, test must pass
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
• I acknowledge that all my contributions will be made under the project's license.

Notes: