Algorithms Exam Practice

This lesson provides comprehensive exam practice for the Algorithms topic, covering the key content from OCR J277 Section 2.2 that appears on Paper 2: Computational Thinking, Algorithms and Programming. This lesson brings together searching algorithms, sorting algorithms, trace tables, and algorithm design.

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Paper 2 Overview for Algorithms

The OCR J277 Paper 2 exam is worth 80 marks and lasts 1 hour 30 minutes. The algorithms section typically accounts for approximately 15–25 marks. Questions range from 1-mark recall questions to 6-mark extended response questions.

Common question types include:

Question Type	Typical Marks	What You Need to Do
Define/State	1–2 marks	Give a precise definition (e.g. "What is an algorithm?")
Describe	2–4 marks	Explain how an algorithm works step by step
Compare	3–4 marks	Identify similarities and differences between algorithms
Trace table	3–5 marks	Complete a trace table for given pseudocode
Write/Complete pseudocode	3–6 marks	Write or complete an algorithm in pseudocode/Python
Evaluate/Recommend	4–6 marks	Justify which algorithm is best for a given scenario

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Practice Question 1: Definitions (2 marks)

Question: Define the term "algorithm" and give one reason why algorithms are used in program development.

Model Answer: An algorithm is a step-by-step set of instructions designed to solve a specific problem or complete a task (1 mark). Algorithms are used in program development to plan the solution before writing code, ensuring the logic is correct and allowing programmers to identify potential issues early (1 mark).

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Practice Question 2: Linear Search Trace (4 marks)

Question: The array data contains: [12, 5, 8, 3, 15, 7]. Trace the following algorithm when searching for the value 15.

target = 15
for i = 0 to data.length - 1
    if data[i] == target then
        print("Found at " + str(i))
    endif
next i

Model Answer:

i	data[i]	data[i] == 15?	Output
0	12	No
1	5	No
2	8	No
3	3	No
4	15	Yes	"Found at 4"
5	7	No

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Practice Question 3: Binary Search Description (3 marks)

Question: Describe how binary search would find the value 42 in the sorted list [10, 20, 30, 42, 50, 60, 70].

Model Answer:

1. Find the middle element: index 3, value 42.
2. Compare 42 with target 42 — they are equal.
3. The item is found at index 3 after one comparison.

(In this case the target happens to be the middle element. For a harder example where multiple steps are needed, always show low, high, mid at each step.)

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Practice Question 4: Sorting Comparison (4 marks)

Question: A company needs to sort a database of 100,000 customer records. Compare the suitability of bubble sort and merge sort for this task.