Merge sort
Lesson details
Learning outcome
I can perform a merge sort to order a list.
Key learning points
- Merge sort splits items in lists into individual lists before merging pairs of lists together till all items are sorted.
- Merge sort is an efficient “divide and conquer” algorithm that can perform well in real world use.
- A merge sort algorithm is usually faster to execute but more complex to write than bubble sort.
- Executing a merge sort takes up extra space in memory.
Keywords
Merge sort - a sorting algorithm that works by repeatedly splitting data into sublists and merging pairs of sublists, ordering the items as they are merged
Splitting - the initial step of dividing an unsorted list into smaller sublists
Merging - the process of combining two already sorted lists into a single, larger sorted list
Common misconception
Merge sort is the most efficient sorting algorithm for all cases.
For smaller data sets, simpler algorithms such as insertion sort or bubble sort can be faster due to the overhead in merge sort of having to break apart the data to be sorted.
Teacher tip
The steps of algorithms should be modelled with explanation from the teacher at every step. Pupils can understand processes better when understanding the detail of what is required at each stage.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.What sorting algorithm repeatedly compares pairs of values within a list and swaps them if they are out of order?
Q2.What happens if two adjacent items are in the wrong order in bubble sort?
Q3.What is a "pass" in bubble sort?
Q4.When does bubble sort stop making passes?
Q5.Which of these is a disadvantage of bubble sort?
Q6.Place the steps of bubble sort in the correct order:
Assessment exit quiz
6 Questions
Q1.What is the first step in a merge sort?
Q2.Match the terms to their definitions:
a sorting algorithm that splits and merges data
dividing a list into smaller parts
combining sorted sublists into a single list
Q3.What is the purpose of merging in merge sort?
Q4.Place the steps of merge sort in the correct order:
Q5.What is one disadvantage of merge sort?
Q6.Which is faster for smaller data sets: merge sort or bubble sort?
To help you plan your 10 computer science lesson on: Merge sort, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 10 computer science lesson on: Merge sort, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 4 computer science lessons from the Searching and sorting algorithms unit, dive into the full secondary computer science curriculum, or learn more about lesson planning.