Tutorials

0 - Common Pseudocode Tasks & FAQs 1 - Input Output 2 - Variables & Constants 3 - Arithmetic Operators 4 - Logical Operators 5 - Boolean Operators 6 - Selection: IF & CASE 7 - Loops: - FOR, WHILE, REPEAT UNTIL 8 - Arrays 9 - Functions & Procedures - Built-in 10 - Functions & Procedures - Custom 11 - Files 12 - Records 13 - ENUMS 14 - Pointers 15 - Sets 15.1 - Creating a Set 15.2 - Adding Elements to a Set 15.3 - Outputting a Set 15.4 - Checking if an Element Exists in a Set 15.5 - Removing an Element from a Set 15.6 - Getting Number of Elements in a Set 15.7 - Converting a Set to an Array 15.8 - Unique Usernames 15.9 - Unique Words 15.10 - Phonetic Alphabet Test 15.11 - Football Players in Both Teams 16 - Object-Oriented Programming - OOP

A set is a data structure that allows us to store data - some key features of sets:

• Unique values - duplicate values are not allowed. If you try to add a duplicate value, it will be ignored (or overwrite the original, depending on the implementation) - you will never get two elements with the same value
• Unordered - unlike arrays, elements in a set aren't ordered (since their location is calculated based on hashing the element), meaning we can't loop through them directly (though most programming languages have a way of e.g. converting a set to an array and looping through the array). We also can't access a set element by an index, like we would an array
• Mutable - we can change the set (add or remove elements) at runtime
• Efficient for certain operations - because of the nature of hashing, certain operations are very fast - adding an element to a set, removing an element from a set and checking if an element exists within a set can all be performed in O(1) time

Hopefully we can see that the use case of a set is therefore slightly different from other data structures like an array or binary tree

In many programming languages, we can also perform common mathematical set operations such as:

• Union: Combining elements of two sets into one (no duplicates).
• Intersection: Finding common elements between two sets.
• Difference: Elements present in one set but not in the other.
• Subset/Superset: Checking if one set is a subset or superset of another.

Some operations you might want to perform are shown in this image - this is also similar to all of the (INNER/OUTER/LEFT/RIGHT etc) JOIN operations you can perform in DBMSs like MySQL

For Cambridge pseudocode, it seems they only require us to define a set for small, e.g. 3 mark questions in paper 3 in A2, rather than actually using set operations, since the official pseudocode guide doesn't actually list a way to add, remove or check if an element exists in a set at runtime. Of course, you can use sets in the real programming language in paper 4 if you want too - so far there has never been a question that's required it, but you are free to use them if it's suitable for that particular question

Note: Cambridge pseudocode doesn't actually specify any syntax/modules for the following features - these have been added simply so people can try using sets in a practical manner themselves, rather than just declaring them. In paper 3 exams, you should only be asked to declare a set using the syntax above, nothing else