OCR GCSE Computer Science J277 - 2.1 Algorithms

Computational thinking

Using methods such as abstraction, decomposition and algorithmic thinking to solve problems.

Abstraction

Removing unnecessary detail so attention is focused on the important information needed to solve a problem.

Decomposition

Breaking a complex problem or system into smaller, more manageable parts.

Algorithmic thinking

Working out a clear sequence of steps that can solve a problem.

Algorithm

A finite sequence of clear steps for solving a problem.

Input

Data supplied to a system or algorithm.

Process

The operations carried out on input data.

Output

The information or result produced by a system or algorithm.

Purpose of Identifying Inputs, Processes, and Outputs

They help define what the solution receives, what it must do and what it must produce before coding.

Flowchart

A diagram that represents the steps and decisions in an algorithm using standard symbols and arrows.

Flowchart Terminator Symbol

Represents the start or end of an algorithm in a flowchart diagram.

Flowchart Process Symbol

Represents an instruction or operation to be carried out in a flowchart diagram.

Flowchart Decision Symbol

Represents a condition or question that causes the algorithm to follow different paths in a flowchart.

Flowchart Input/Output Symbol

Represents data entering or leaving the algorithm in a flowchart diagram.

Pseudocode

A structured, language-independent way of describing an algorithm using programming-like statements.

OCR Exam Reference Language

OCR's defined pseudocode-style language used to express algorithms consistently in J277 assessments.

Algorithm Language Permissibility in OCR Exams

OCR permits OCR Exam Reference Language or a high-level programming language the student has studied, where the question allows it.

Trace table

A table used to record how variables or other values change while an algorithm is followed step by step.

Usefulness of Trace Tables

They help understand, test and debug algorithms by showing their state as each step executes.

Algorithm Tracing Rule

Follow the instructions exactly in order and update values only when the algorithm changes them.

Searching algorithm

An algorithm used to find a target item in a collection of data.

Linear search

Checks items one at a time in order until the target is found or all items have been checked.

Linear Search Data Requirement

Does not require sorted data.

Binary search

Repeatedly compares the target with the middle item and discards half of the remaining search area.

Binary Search Data Requirement

The data must be sorted.

Efficiency Advantage of Binary Search

Each comparison can eliminate about half of the remaining items on a large sorted list.

Sorting algorithm

An algorithm that arranges data into a specified order.

Bubble sort

Repeatedly compares neighbouring items and swaps them when they are in the wrong order until the list is sorted.

Pass of Bubble Sort

Adjacent pairs are compared and swapped where necessary across the list.

Insertion sort

Builds a sorted section by taking each next item and inserting it into the correct position.

Growth Mechanism of Insertion Sort

One item at a time is placed into its correct position within the already sorted section.

Merge sort

Repeatedly divides data into smaller groups, then merges the groups back together in sorted order.

Central Idea of Merge Sort

Divide the list, then combine the smaller sorted parts to form