FAQ: Merge Sort: Conceptual - Merging

Frequently Asked Questions Python FAQ
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This community-built FAQ covers the “Merging” exercise from the lesson “Merge Sort: Conceptual”.

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This exercise can be found in the following Codecademy content:

Sorting Algorithms

FAQs on the exercise Merging

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2

Since no one answered this question:

lists must be sorted before merging because the purpose of merge is to merge two sorted lists to create a new sorted list, without having to perform another sort. Merging can be done in linear time, while sorting is O(n*log(n)) .

1 Like
3

What’s the answer to this question:
Why is it important that we only merge pre-sorted lists?
I don’t know the answer.

4

Please can you explain how you arrived at O(nlogn) for sorting? I’m guessing it has something to do with splitting the list into two with which recursive call, but I’m not sure how exactly you would arrive at O(nlogn) based on just that.

5

because while merging you are always sorting on halves.
And it uses the same loop to traverse both list every step as it is using 2 variable left and right at the same time.
Each step linearly traversed on halves O(nLogn)

6

if its not pre sorted you cant merge both with comparing left and right variable together in a loop. It might face a smaller number in farther down the line in the same list