IB Computer Science HL · Year 2 · Lesson 2
Stacks: LIFO operations and trade-offs
Data structures organize information so that operations are efficient, understandable and appropriate to the problem.
Paper 250 minutesB2.2.3
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Today’s targets
What you need to be able to do
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- ExplainThe concept of a stack as a “last in, first out” (LIFO) data structure
B2.2.3
Paper 2 lensMatch the depth of every response to the command term. Previously learned content can move quickly, but retrieval must still be accurate.
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Retrieve
Rapid Recall Deck
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Say the answer aloud before flipping. Mark secure knowledge quickly and spend time on the gaps.
- What does LIFO mean for a stack?: Last in, first out: the most recently pushed item is the first item removed.
- What does push do to a stack?: Push adds an item to the top of the stack.
- What do pop, peek, and isEmpty do?: pop removes and returns the top item; peek returns the top item without removing it; isEmpty checks whether the stack contains no items.
- When is a stack an appropriate data structure?: When the most recent item must be processed first, such as undo history, function-call management, or backtracking.
- How do stack operations affect performance and memory?: Operations at the top are typically very fast, while memory use grows with the number of stored items and the implementation used.
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B2.2.3 · Learn
Core knowledge and application
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B2.2.3Explain
The concept of a stack as a “last in, first out” (LIFO) data structure
Data structures organize information so that operations are efficient, understandable and appropriate to the problem.
Exam moveGive the mechanism or relationship and make the reasons/causes explicit.
Required detail 1Must include fundamental operations such as push, pop, peek and isEmpty
Required detail 2How stack operations impact both performance and memory usage
Required detail 3An appropriate stack for a specific problem
Assessment boundaryStacks/queues are assessed conceptually at the “explain” level; operations may be defined in an algorithmic-thinking question. Paper 2
Explain it without notes
Explain: The concept of a stack as a “last in, first out” (LIFO) data structure in the context of a scheduling application with changing data.
- Must include fundamental operations such as push, pop, peek and isEmpty
- How stack operations impact both performance and memory usage
- An appropriate stack for a specific problem
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Apply
Transfer to a new scenario
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ScenarioA scheduling application with changing data needs a design or technical decision related to today’s topic. Explain what matters and why.
- Must include fundamental operations such as push, pop, peek and isEmpty
- How stack operations impact both performance and memory usage
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Exam lens
Paper 2 practice
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Build the response before checking notesUse precise terminology and match the required depth.
- Explain: The concept of a stack as a “last in, first out” (LIFO) data structure in the context of a scheduling application with changing data.
Self-checkAnswer the exact command term. For explain, include mechanism/reason; for compare, pair criteria; for discuss/evaluate/justify, build supported reasoning and a conclusion.
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Homework
Finish the learning cycle
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IA — main task
Refine Criteria A/B/C. Use today’s lesson to make the problem specification, decomposition, algorithms or testing plan more precise where relevant.
Syllabus — 10–15 min
Repeat the recall deck and complete the lesson response prompt without model support.
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End of Lesson 2.