…and memory efficiency

"You’re given an array of numbers. You have to add up all the numbers and return the total."
 
Replaced ArrayList<Integer> with a primitive int[] in the recursive sum method to improve performance and reduce memory usage.
- Faster execution: Avoids boxing/unboxing and uses direct array access.
- Lower memory usage: Primitive arrays are lighter than ArrayList with boxed types.
- Simpler code: No need for imports or list management for fixed-size data.
This version is ideal for static numeric datasets where performance and clarity are priorities.