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CS Lesson 3
Making hot buttered toast the way Mr. Creighton does... (the proper way)
Making hot buttered toast the way Mr. Creighton does... (the proper way)
Task 1: Can you make toast?
Task 1: Can you make toast?
Students launch straight into the toast sequencing activity:
Student instructions: Click the toast pic
Arrange the instructions into an algorithm for making buttered toast.
Work from what you already know about making toast
Rebuild Mr Creighton’s exact 21-step toast-making sequence, from first to last. Every step must be in its specified position. If even one is wrong, you will see “Incorrect” and all the cards will be shuffled back.
Why was Task 1 so hard?
Why was Task 1 so hard?
You already know what making toast looks like. But knowing the result is different from explaining every instruction needed to produce it.
With 21 mixed-up instructions, you had to keep track of many details and work out which actions depended on others. Your brain may also have filled in steps automatically because the task felt familiar.
COMPUTER SCIENCE · KEY IDEAS
ABSTRACTION
Focus on what matters for the problem.
ABSTRACTION
Focus on what matters for the problem.
Abstraction means keeping the important information and leaving out details that are not needed for a particular purpose.
Toast example: Your algorithm needs to say when to put the bread in the toaster. It does not need to describe the colour of the plate.
Ask yourself: “Which details affect how this solution works?”
COMPUTER SCIENCE · KEY IDEAS
PATTERN RECOGNITION
Look for similarities that help you reuse a solution.
PATTERN RECOGNITION
Look for similarities that help you reuse a solution.
Pattern recognition means identifying repeated features, steps or structures within a problem or across different problems. These similarities can suggest a reusable rule or approach, which must be tested in the new situation.
Toast example: Making toast and making a sandwich share a pattern: prepare → make → tidy up → serve. The overall approach can be reused, but the detailed instructions change.
Ask yourself: “Have I solved something similar? What can I reuse, and what needs to change?”
COMPUTER SCIENCE · KEY IDEAS
Algorithm
A precise set of instructions for completing a task or solving a problem.
Algorithm
A precise set of instructions for completing a task or solving a problem.
The instructions must be clear enough to follow without guessing. They can include:
Sequence: actions carried out in order.
Selection: a decision that chooses what happens next.
Iteration: repeating instructions, often called a loop.
Why one exact sequence?
Why one exact sequence?
A completed algorithm can look obvious. Creating its precise steps from scratch is harder.
Another algorithm might also make toast. Here, your challenge is to reconstruct this particular algorithm exactly. A deterministic algorithm follows the same steps and gives the same result each time when its inputs and conditions are the same.
Task 2
Task 2
Task 3
Task 3
WHAT IS AN ALGORITHM?
An algorithm is a precise set of instructions for completing a task or solving a problem.
The instructions must be clear enough to follow without guessing. They can include:
Sequence: actions carried out in order.
Selection: a decision that chooses what happens next.
Iteration: repeating instructions, often called a loop.
Remember: Breaking a task into smaller jobs is decomposition. Choosing the relevant details is abstraction. Spotting a structure you can reuse is pattern recognition.
Task 4: Can you make toast?
Task 4: Can you make toast?
Decomposition abstraction and Pattern recognition of the toast problem
Set up the kitchen
Make the Toast
Clean up
Leave and eat
Look at the picture of the steps broken down and then lets have another go at making toast....
Using algorithms to rank data - websites
Using algorithms to rank data - websites
Why do we need algorithms to search the internet?
Imagine searching “how to fix a bike chain” and getting thousands of links in random order. How long would it take to find one that actually helps?
A search engine uses algorithms to find pages that match your search and rank them. It looks for clues about which pages are most likely to help, so you can start with a few useful results instead of checking every link yourself.
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