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Course 267 · Digital course 30

Choose Stacks, Queues and Graphs

Build a runnable fictional help-desk simulator with an undo stack, FIFO queue and small dependency graph, plus empty and cyclic case tests. Work from supplied original examples and check changed cases.

Before you start

Complete or review Programming with Python before starting.

Programming with Python See everything you’ll need

Free download · Original practice data · No external account required. Download the starter pack

What you’ll leave with

A runnable fictional help-desk simulator with an undo stack, FIFO queue and small dependency graph, plus empty and cyclic case tests.

Start course Start without an account. Sign in to save lesson progress across devices.

Your project

Start with the practice files. Build your project one lesson at a time.

Practice files are free without an account. Sign in to save your project record in My Proof: a description, checklist, and optional work link. Keep the original files in your own app or notebook; saving a project record does not upload them.

  1. Get your materialsDownload practice filesSupplied practice cases, a blank working record, complete lesson instructions, and annotated worked examples.
  2. Make your projectView the project checklist Work in your own notebook, document, or software. Use the supplied practice examples when you prefer.
  3. Keep a private recordSave a project record Sign in to save a description and checklist, then return to update them.
Course handbook

Know the route before you begin.

Here’s what you’ll need and what you’ll make. You can return to this guide during any lesson.

Who this is for

Learners ages 14+ and adults ready for the named prerequisite; no employment or private records required.

Prepare before lesson one
  • Complete or review Programming with Python before starting.
  • Use a local text editor and a free Python 3.10+ interpreter for Python files, or a current browser for HTML files. Supplied code uses no paid services or external packages.
  • Create a fresh practice folder and use only the supplied fictional inputs. A paper trace is labeled a trace, not an executed test.
Your final project

Finish with proof you can use.

A runnable fictional help-desk simulator with an undo stack, FIFO queue and small dependency graph, plus empty and cyclic case tests.

Save a project record in My Proof
See project checklist and review criteria

Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.

What to include

  • An operation-to-structure map with three distinct retrieval rules.
  • An undo trace with last-in-first-out and empty-state handling.
  • A FIFO record with clear empty behavior.
  • A four-node dependency plan ending with archive.
  • A cycle diagnosis and justified repair record.
  • A runnable stack/queue/dependency demonstration with boundary evidence.

Review and revise

Use these criteria to check your work and choose what to improve.

  • The implementation or declared simulation follows the supplied contract and retains inspectable original inputs.
  • Normal, boundary and rejected cases are recorded with expected versus observed results.
  • The changed case has a correct explanation and does not rely on hidden state.
  • The project includes source, outputs, instructions and honest tool, privacy and verification limits.
Three ideas to help you along the way
Three useful ideas

The rules behind the steps.

01

State the contract

Name inputs, permitted states and observable outputs before editing the implementation.

02

Preserve the evidence

Keep the actual source, changed input and expected/observed record so someone can repeat the work.

03

Test the boundary

Check a rejection or changed case and distinguish local practice from real service or native-tool behavior.

What do these words mean?
Key words

Key terms worth knowing.

Stack
A last-in-first-out container.
Queue
A first-in-first-out waiting structure.
Predecessor
A node that must finish before another.
Cycle
A dependency path that returns to an earlier node.
Your route

6 lessons.
One useful project.

Work in order the first time. Each lesson makes something the next lesson can use.

  1. 1
    Up next

    Model operations before containers

    Use the supplied case to model operations before containers and retain an inspectable operation-to-structure map with three distinct retrieval rules.

  2. 2
    19 min

    Trace and implement a stack

    Use the supplied case to trace and implement a stack and retain an inspectable undo trace with last-in-first-out and empty-state handling.

  3. 3
    19 min

    Implement a fair FIFO queue

    Use the supplied case to implement a fair fifo queue and retain an inspectable FIFO record with clear empty behavior.

  4. 4
    19 min

    Represent dependencies as a graph

    Use the supplied case to represent dependencies as a graph and retain an inspectable four-node dependency plan ending with archive.

  5. 5
    22 min

    Detect repeated visits and cycles

    Use the supplied case to detect repeated visits and cycles and retain an inspectable cycle diagnosis and justified repair record.

  6. 6
    24 min

    Compare structures with a test matrix

    Use the supplied case to compare structures with a test matrix and retain an inspectable runnable stack/queue/dependency demonstration with boundary evidence.

Use the tools

Tools to help you practice.

See all tools
ZIP · practice files

Choose Stacks, Queues and Graphs practice files

Supplied practice cases, a blank working record, complete lesson instructions, and annotated worked examples.

Text worksheet

Your course project worksheet

A downloadable text worksheet with each lesson’s working output, space for your answers, and the shared final-project checklist. Save your own copy.

Source transparency

Sources and further study.

Explore the references behind the lessons and take your learning further. Source notes explain access and reuse.

docs.python.org — data structures.html
Source & access notes · checked 2026-10-01

Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.

Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.

Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.

docs.python.org — collections.html
Source & access notes · checked 2026-10-01

Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.

Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.

Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.

docs.python.org — graphlib.html
Source & access notes · checked 2026-10-01

Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.

Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.

Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.

Ready when you are

Start with the first useful move.

You’ll always know what to do, what to make, and where to go next.

Start lesson one