Your solution for "Subarray Sum Equals K" is excellent. Here are some strengths and minor suggestions:

Strengths:

• You have correctly implemented the optimal solution using a hash map to store cumulative sums.
• The code is well-commented, explaining the approach clearly.
• You handled the edge case by initializing the map with (0,1).
• The use of map.getOrDefault is efficient and concise.

Areas for Improvement:

• There are no major issues. However, you might consider using a for-each loop for iterating over nums to make the code slightly more concise. For example:

  for (int num : nums) {
      rSum += num;
      // ...
  }

  But this is a minor stylistic point and does not affect correctness.

• The variable name cmp might be slightly ambiguous. Consider renaming it to something like complement or target to make it more descriptive. However, it is understandable in context.

Overall, your solution is correct and efficient.