The solution for "Subarray Sum Equals K" is excellent. It correctly uses the prefix sum technique with a hash map to achieve optimal time and space complexity. The code is clear and concise. However, note that the student included two additional solutions for other problems in the same submission. For future submissions, it is important to only include the solution for the problem being evaluated to avoid confusion.

One minor suggestion: although the code is correct, you might consider adding a brief comment explaining the purpose of the complement variable to enhance readability for others who may review the code.

Overall, the solution for the target problem is correct and efficient.