AQA Computer Science Paper 1

Algorithm

A step-by-step set of instructions that can be followed to solve a problem.

Computer Program

An implementation of an algorithm using a specific programming language.

Decomposition

The process of breaking down a problem into smaller, more manageable sub-problems that each accomplish a specific task.

Abstraction

The process of removing unnecessary details to focus on the essential parts of a problem.

Pseudocode

A way of describing algorithms using structured, plain English.

Program Code

Code written in a specific programming language.

Flowchart

A diagram that represents an algorithm using symbols.

Efficiency

A measure of how well an algorithm performs in terms of time or steps.

Searching Algorithm

A method used to find a specific value (target) in a list of data.

Linear Search

A search method that checks each item one by one.

Binary Search

A fast search method that works on sorted data by halving the search range on each iteration.

Sorting Algorithm

A method used to arrange data into a specific order, usually ascending or descending

Bubble Sort

A simple sorting algorithm that repeatedly swaps adjacent items.

Merge Sort

A fast, efficient sorting algorithm that uses divide-and-conquer.

Divide and Conquer

The process of repeatedly splitting a dataset into smaller datasets and so on

Why is binary search better than linear search for a large array?

• Binary search is more efficient on average

• A linear search would be less efficient because it must check all items

What are advantages and disadvantages of bubble sort and merge sort?

Bubble

• A: simpler to code

• A: quicker to sort smaller list

• D: slower to sort larger arrays

• D: less efficient

Merge

• A: more efficient

• A: quicker to sort larger arrays

• D: harder to code

Procedure

A subroutine that performs an action but doesn't return a value.

Function

A subroutine that returns a value.

Robustness

How well a program can handle errors or unexpected inputs.

Data Structure

A concept referring to ways of organizing and storing data.

What is an array

a data structure that stores a collection of items, typically of the same data type, accessed using an index (one- and two-dimensional are required).

• a collection of similar data items stored under a single name

• each item is accessed using an index

Records

A data structure used to group related data items of potentially different data types under a single name.

Concatenation

An operation to join two or more strings together.

Local Variables

Variables declared within a subroutine that only exist while the subroutine is executing and are only accessible within that subroutine.

Syntax Error

An error in the grammar or rules of the programming language, preventing the code from being translated or run

code from being translated or run.

Logic Error

An error in the program's design or algorithm that causes it to produce incorrect or unexpected results, even if it runs without crashing.

Advantages of decomposition?

• It makes complex problems easier to understand

• Easier to design and implement solutions for

• Easier to debug and maintain

• Allows sub-problems to be split across a team of developers

Advantages of abstraction?

• focus on essential aspects of the problem

• time is not wasted on developing unnecessary components

What factors affect speed of sorting algorithms?

• size of data set

• nature of data

• algorithms design (bubble sort slower/merge sort faster; linear search slower/binary search faster)

Efficiency increases when?

• number of steps is lower

• algorithm avoids unnecessary operations

Linear search vs Binary search

Linear

• any data (unsorted)

• slower (checks one by one)

• simple

Binary

• sorted data

• faster (halves list each step)

• more complex to implement

How does linear search work?

• start at first item in list

• check each item one by one until target is found or end is reached

How does binary search work?

• can only be used on sorted lists

• repeatedly divides list in half, comparing middle element to target (divide and conquer)

• narrow search range until item is found (as middle element) or the list cant be divided further

How does bubble sort work?

• repeatedly goes through list, comparing 2 adjacent items and swapping if they are in wrong order

• this is done as multiple passes until no swaps are needed - indicating the list is sorted

Characteristics of bubble sort

• simple to understand and implement

• inefficient for large data sets as it requires multiple passes

• takes a long time if list is in reverse order

How does merge sort work?

divide and conquer algorithm

• continuously splits the list in half until each sublist has one item

• merge sublists back together in correct order

Characteristics of Merge Sort

• faster than bubble sort for large datasets

• uses more memory due to recursion and temporary lists

• more complex to implement

Why do data types matter?

• help computer understand how to store and manipulate data

• choosing correct data types ensures the program runs efficiently and without errors

• some operations are only valid for certain data types

What is a subroutine?

• a block of code given a unique name that can be called multiple times

• may include parameters and return values

Why are meaningful identifier names important?

improves readability and understanding

Characteristics of Array

• items must be same data type

• indexing starts at 0 (for most languages)

Array vs Records

array

• data types - all elements must be the same

• accessed by - index

• suited for - list of similar items

records

• data types - can be different

• accessed by - field name

• suited for - grouping related attributes

What is structured programming?

method of writing clear, modular, and easy-to-understand code using 3 core principles:

• sequence

• selection

• iteration

Define the 2 types of subroutine

• procedure - performs an action

• function - performs an action and returns a value

Characteristics of local variables

• declared inside a subroutine

• can only be accessed within parameters of the subroutine

• only exist while the subroutine is executing

Advantages of Subroutines

• can be developed in isolation/independently/separately

• easier to discover errors

• easier to understand program code

• easier for a team of programmers to work together on a large project

• easier to reuse code

Data validation checks

• length check

• presence check

• range check