Breaking Problems Down

Break big problems into smaller parts that are easier to understand, solve and test.

About 3 min read
  • Define decomposition
  • Break a problem into smaller tasks
  • Explain the benefits of decomposition
Before you start

You know that computers follow algorithms step by step. Before writing an algorithm, you need to understand the problem.

Solve one part at a time

Big problems can feel impossible at first. Decomposition means splitting a problem into smaller parts. Each part is easier to think about and solve. When every part works, you can join them to solve the original problem. Teams can also share the work, with each person building a separate part.

Definition: decomposition

Breaking a problem down into smaller, more manageable parts.

Definition: subproblem

A smaller problem that forms part of a larger one.

Decomposing a game

A quiz game may sound like one large task, but it contains smaller ones: storing questions, showing a question, reading an answer, checking the answer, updating the score and showing the result. Each part can be built and tested on its own.

Plan a school website

Decompose the task of creating a school website.

  1. Plan the pages that are needed.
  2. Write the content.
  3. Design the layout.
  4. Add photos and links.
  5. Test the website on different devices.

Answer: One large task is now five smaller tasks.

Stop when a task is clear

Keep breaking a problem down until each part is small enough to solve directly.

Exam focus
Say it like this“Decomposition makes each part easier to solve and test.”
Not like this“It makes the problem simple.” — State the exact benefit.
Common mistakeListing the parts in a random order or naming a benefit without explaining it.

Practice

What is decomposition?
Breaking a large problem into smaller parts.
Give one benefit of decomposition.
Each part is easier to solve and test, and teams can share the work.
Break making a sandwich into four smaller steps.
For example: get the bread, add the filling, close the sandwich and cut it.
Going further
Decompose a program that records homework and warns when work is due tomorrow.
Parts include adding homework, storing tasks, reading today's date, comparing due dates and displaying warnings.

Quick check

Decomposition quick check

What does decomposition do to a problem?

Each smaller task can then be understood and solved separately.

Why does decomposition help teams?

Separate tasks can be shared, then joined together when they work.

Which is a good subproblem of a quiz game?

It is one clear job that can be written and tested alone.
Key takeaways
  • Decomposition breaks a problem into smaller parts.
  • Smaller parts are easier to solve and test.
  • Teams can work on different parts.
  • Stop when each part is clear.
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