Algorithms | OCR GCSE Computer Science (J277)
Algorithms
- 81 questions
- 5 subtopics
- J277/02
- J277/02
Algorithms is examined in J277/02, Computational thinking, algorithms and programming.
It covers abstraction, decomposition and algorithmic thinking, Flowcharts, pseudocode and structure diagrams, trace tables and correcting algorithms, linear and binary search and bubble, merge and insertion sort.
Sample questions from Algorithms
Answer each one closed book first, then open the answer.
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Abstraction, decomposition and algorithmic thinking
What can go wrong if abstraction removes too much detail?
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A model that ignores an important detail gives inaccurate results. A weather forecast that left out wind speed would make poor predictions. -
Abstraction, decomposition and algorithmic thinking
Why must every step of an algorithm be unambiguous?
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A computer follows each instruction exactly and cannot guess what was meant. A vague step could be followed in different ways and give different results. -
Flowcharts, pseudocode and structure diagrams
Define the term pseudocode.
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Pseudocode is a way of writing an algorithm in structured, English-like statements. Pseudocode does not follow the strict syntax of any one programming language. -
Flowcharts, pseudocode and structure diagrams
How is a sub program shown in a flowchart?
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A sub program is drawn as a rectangle with an extra vertical line down each side. The sub program's own steps can be set out in a separate flowchart. -
Trace tables and correcting algorithms
Which values appear in the total column of a trace table for total = 0, for i = 1 to 3, total = total + i * i, next i?
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The total column shows 0, then 1, 5 and 14. Each pass adds the square of i, so the final value of total is 14. -
Trace tables and correcting algorithms
Why does the loop count = 1, while count <= 5, print(count), endwhile never end, and how is it fixed?
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The variable count stays at 1, so the condition is always true and the loop is infinite. A line count = count + 1 must be added inside the loop. -
Linear and binary search
A linear search looks for 15 in [8, 3, 15, 6, 11]. Which items are checked?
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The search checks 8, then 3, then 15. The target is found at index 2 after three comparisons. -
Linear and binary search
What are the advantages of a binary search over a linear search?
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A binary search is much faster on large lists. Each comparison removes half of the remaining items, so few comparisons are needed.
The 5 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Abstraction, decomposition and algorithmic thinking | Computational thinking, abstraction and decomposition with worked examples, algorithmic thinking, what an algorithm is, and how the principles work together to solve a problem. | 16 |
| Flowcharts, pseudocode and structure diagrams | Inputs, processes and outputs, structure diagrams, pseudocode, the flowchart symbols for decisions, inputs and outputs, sub programs and loops, and nesting. | 16 |
| Trace tables and correcting algorithms | Trace tables and why they are used, the output of short algorithms in Exam Reference Language, and finding and fixing errors in given code. | 16 |
| Linear and binary search | How linear and binary searches work, why a binary search needs sorted data, the midpoint calculation, worked searches through short lists, and the strengths of each. | 16 |
| Bubble, merge and insertion sort | How bubble, merge and insertion sorts work, worked passes through short lists, merging two sorted lists, and how the three sorts compare. | 17 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
OCR GCSE Computer Science Active Recall Guide
Every topic, not just this one. 740 questions with their answers.