Merge two sorted arrays in-place

Given two arrays arr1 and arr2, both sorted in ascending order.

• Modify arr1 in-place to contain all elements from arr1 and arr2 in ascending order.
• Do not allocate an additional array for the merge result.

Assumptions/clarifications you may use:

• arr1 has enough extra capacity at the end to hold all elements of arr2 (e.g., arr1 length is m + n , where the first m entries are valid and the last n are empty slots), and arr2 has length n .
• You are given m and n .

Follow-ups:

1. How would you adapt your approach if both arrays were sorted in descending order?
2. If the arrays were not sorted , what would you do (and what are the time/space trade-offs)?

Define the time and space complexity of your approach.