Merge Sort

Test yourself

Merge Sort

Merge sort is an example of a divide and conquer algorithm, where the problem is broken down into smaller steps.

The concept

If we have two packs of cards, which are both already in order and want to combine them, what can we do?
One solution is to only consider the top card of each pile, and create a new deck starting from the smaller of the two cards.
This will give us a combined sorted pack.
This is called merge sort.

In English

Split the lists into lists of size one.
Merge each pair of sublists by comparing the first value of each list and putting the smaller value into the new list first.
Continue merging until there is only one list.
It is always the first two items of two adjacent lists that are being compared.
Some lists may end up one-sided, where many more numbers in one list are compared with fewer numbers in another for the final merge. That is ok! The lists do not always need to remain balanced.

Example

We will sort the list [12, 5, 9, 1] using merge sort.
Step 1: Split the list until each piece has one element
Step 2: Merge [12] and [5]
- 5 < 12 → 5 'comes down'
Step 3: Merge [12] and [ ]
- 12 'comes down'
Step 4: Merge [9] and [1]
- 1 'comes down'
Step 5: Merge [9] and [ ]
- 9 'comes down'
Step 6: Merge [5, 12] and [1, 9]
- Compare first items
- 5 > 1
- 1 'comes down'
Step 7: Compare first items
- 5 < 9
- 5 'comes down'
Step 8: Compare first items
- 12 > 9
- 9 'comes down'
Step 9:
- 12 comes down

Pros and cons of merge sort:

Pros:
- A very efficient algorithm.
Cons:
- Can be slower for small lists.
- Needs additional memory.

1Computer Systems

1.1Systems Architecture

1.1.1Fetch-Execute Cycle

1.1.2Common CPU Components & Their Function

1.1.3Von Neumann Architecture

1.1.4Factors Affecting CPU Performance

1.1.5Embedded Systems

1.1.6Exam-Style Questions - Von Neumann Architecture

1.1.7Diagnostic Misconceptions - Embedded vs General

1.2Memory & Storage

1.2.1Types of Memory

1.2.2Flash Memory

1.2.3Properties of Flash Memory

1.2.4Running Out of Memory

1.2.5Virtual Memory

1.2.6Units of Capacity

1.2.7Calculating Capacity Requirements

1.2.8Solid State Storage

1.2.9Properties of Solid State Media

1.2.10Magnetic Storage

1.2.11Properties of Magnetic Media

1.2.12Examples of Magnetic Storage

1.2.13Optical Storage

1.2.14Properties of Optical Media

1.2.15Examples of Optical Storage

1.2.16Types of Optical Disk

1.2.17Number Bases

1.2.18Converting Number Bases

1.2.19Hexadecimal

1.2.20Using Hexadecimal

1.2.21Converting Denary & Hexadecimal

1.2.22Binary Addition

1.2.23Binary Shifts

1.2.24Representing Text

1.2.25ASCII & Unicode

1.2.26Representing Images

1.2.27Converting Binary & Images

1.2.28Representing Sound

1.2.29Data Compression

1.2.30Grade 9 - Storage

1.2.31Exam-Style Questions - Primary Memory

1.2.32Exam-Style Questions - Storage

1.2.33Exam-Style Questions - Data Conversions

1.2.34Diagnostic Misconceptions - RAM vs ROM

1.2.35Diagnostic Misconceptions - Bits, Nibbles & Bytes

1.2.36Diagnostic Misconceptions - Bits Required to Store

1.2.37End of Topic Test - Computer Systems

1.2.38End of Topic Test - Representation

1.3Computer Networks, Connections & Protocols

1.4Network Security

1.4.1Forms of Attack

1.4.2Penetration Testing

1.4.3Malware

1.4.4How Malware Spreads

1.4.5Social Engineering

1.4.6Phishing

1.4.7Cracking Passwords

1.4.8Denial of Service Attacks

1.4.9Data Interception

1.4.10Methods of Data Interception

1.4.11SQL Injection

1.4.12Network Administration

1.4.13Network Forensics

1.4.14Protecting Against Malware

1.4.15Firewalls

1.4.16User Access Levels

1.4.17Passwords

1.4.18Encryption

1.4.19End of Topic Test - Networks

1.5Systems Software

1.5.1System Software

1.5.2Utility Software

1.5.3Operating Systems

1.5.4User Interfaces

1.5.5Memory & Process Management

1.5.6File Management

1.5.7Device Management

1.5.8User Management

1.5.9Encryption Software

1.5.10Defragmentation Software

1.5.11Data Compression Software

1.5.12Backup Software

1.6Ethical, Legal, Cultural & Environmental Concern

2Computational Thinking, Algorithms & Programming

2.1Algorithms

2.1.1Computational Thinking - Abstraction

2.1.2Computational Thinking - Decomposition

2.1.3Algorithmic Thinking

2.1.4Pseudocode

2.1.5Flowchart Diagrams

2.1.6Interpreting Algorithms

2.1.7Correcting Algorithms

2.1.8Completing Algorithms

2.1.9Search Algorithms

2.1.10Binary Search

2.1.11Linear Search

2.1.12Overview of Sort Algorithms

2.1.13Bubble Sort

2.1.14Merge Sort

2.1.15Insertion Sort

2.1.16Exam-Style Questions - Sorting Algorithms

2.2Programming Fundamentals

2.3Producing Robust Programs

2.3.1Defensive Design

2.3.2Validation & Sanitisation

2.3.3Authentication & Contingencies

2.3.4Maintainability

2.3.5Purpose of Testing

2.3.6Types of Testing

2.3.7Test Plans

2.3.8Types of Errors

2.3.9End of Topic Test - Programming

2.3.10Exam-Style Questions - Testing

2.4Boolean Logic

2.4.1Binary Systems

2.4.2Logic Circuits

2.4.3Boolean Logic

2.4.4Boolean Operators

2.4.5Grade 9 - Logic

2.5Programming Languages & IDEs

2.5.1High-Level vs Low-Level Languages

2.5.2Translation - Compliers & Interpreter

2.5.3Translation - Assemblers

2.5.4Integrated Development Environments

2.5.5Exam-Style Questions - Translation

Jump to other topics