Merge Sort Interview Questions and Answers

Merge sort is the sorting technique used to divide the array into sub-arrays and then sort those sub-arrays after that, it merges the all-sorted arrays into a single sorted array. This article covers all the important and interview-related question answers that will help you to clear the interview rounds.

Merge Sort Interview Questions and Answers

Here are the top interview question answers on the Merge Sort:

1. What is the good time to use Merge Sort?

Merge Sort is used when we don't know the size of the data, and also we can apply it to any size of data. But if we have less data, then Quick Sort performs better, and at that time, the data is uniformly distributed.

2. Why is Merge Sort stable?

When we use merge sort with items that have the same value then It can contains their original sequence. Suppose we are sorting cards by number and we have two 7s, the first seven will still come before the second seven in a final sorted list.

3. Can we say Merge Sort in place?

No, Merge Sort is using extra space. It utilizes extra memory as other arrays for storing data temporarily while sorting and merging stuff.

4. How do Merge Sorts handle the sorted elements?

It is the same as the Quick Sort. Merge Sort always maintains the same speed when the data is sorted or not, and It always performs equally.

5. What is the time complexity of Merge Sort?

Merge Sort works by iterating over your data several times. In each iteration, it merges more and more larger sorted chunks, with the chunks doubling in size each time. To sort n items, it needs logn iterations, and each iteration will need to do n operations, which gives us the overall time complexity of O(n log n).

6. What is the use of divide-and-conquer in Merge Sort?

It does this by dividing the problem into smaller and smaller pieces. It first divides the data into smaller and smaller groups until it has individual pieces. Then, it combines these groups back together in order.

7. Is Merge Sort quicker with partially sorted data?

No, Merge Sort takes the same time whether or not the data is partially sorted. It goes through the same steps each time.

8. How is Merge Sort better or worse compared to other sortings?

Though Merge Sort is reliable and stable (with time complexity O(n log n)), it's not the best every time. Its principal disadvantage is that it requires additional memory space. Quick Sort would generally be the preferred option, and in certain special situations, Bucket and Radix Sort maybe even more suitable.

9. Do we use Merge Sort for linked lists?

Yes, Merge Sort is fine with linked lists. Because linked list elements are not stored side by side in memory, you simply have to watch out for managing the links between elements.

10. When is Merge Sort slowest?

Merge Sort is slowest when it has to compare alternate elements, such as when comparing [1,3] and [2,4]. This takes the most comparisons when merging.

11. Can we make Merge Sort less memory-intensive?

Yes, you can do that by making it reuse one temporary array rather than creating a new one every time you merge. It still requires additional space, but this is more efficient.

12. How does Merge Sort treat duplicate values?

It manages duplicates nicely. During merging, if it encounters equal values, it places the ones on the left first, which maintains them in their original order.

13. Why is Merge Sort appropriate for linked lists?

It suits linked lists as it only needs to alter the pointers between elements. Quick Sort would have to traverse the list extensively, which is slow using linked lists.

14. What are the various types of Merge Sort?

There's a two-way Merge Sort, which divides data into pairs, and a multi-way Merge Sort, which can divide into more parts simultaneously. Multi-way is especially helpful when sorting extremely large files.