Description

This PR adds an implementation of the "Subarray Sum Equals K" algorithm to thegeneral module. The algorithm counts the number of contiguous subarrays that sum to exactlyk.

Implementation Method:

• Uses prefix sum technique with HashMap for O(n) time complexity
• Space complexity: O(n) for the HashMap
• Handles edge cases including empty arrays, negative numbers, and zero sums

Algorithm Reference:
This is a classic LeetCode problem (Problem 560). The solution uses the prefix sum approach where we track cumulative sums and check ifprefix_sum - k exists in our map, which indicates a subarray with sumk exists.

Type of change

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I ran bellow commands using the latest version ofrust nightly.
• I rancargo clippy --all -- -D warnings just before my last commit and fixed any issue that was found.
• I rancargo fmt just before my last commit.
• I rancargo test just before my last commit and all tests passed.
• I added my algorithm to the correspondingmod.rs file within its own folder, and in any parent folder(s).
• I added my algorithm toDIRECTORY.md with the correct link.
• I checkedCONTRIBUTING.md and my code follows its guidelines.