Celebrity Heads

Just add Computer Science!

AM I HUMAN?

NO

What do Decision trees do?

We can use them for classifying things!

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You just need to ask a series of Yes/No questions to narrow down the possible answers.

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A decision tree where every question has only two options (like yes/no), is called a binary tree.

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What do Decision trees do?

We can use them for classifying things!

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You just need to ask a series of Yes/No questions to narrow down the possible answers.

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A decision tree where every question has only two options (like yes/no), is called a binary tree.

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What questions do you need to ask to figure out

What animal am I thinking of?

as quickly as possible?

What animal am I thinking of?

Does it have hair/fur?

Could you keep it as a pet?

Does it have feathers?

YES

NO

YES

NO

YES

NO

Is it a cat?

YES

NO

Is it a Giraffe ?

YES

NO

Is it a farm animal ?

YES

NO

Does it have legs ?

YES

NO

Is it a reptile?

YES

NO

What animal am I thinking of?

Does it have feathers?

NO

YES

YES

NO

Is it some sort of cat?

YES

NO

Is it a farm animal ?

NO

YES

Does it have legs ?

YES

NO

Is it an amphibian?

YES

Is it an reptile?

YES

NO

Is it tall?

YES

Should you keep it as a pet?

YES

NO

• This decision tree works too!
• It’s not as good as the last one
• Probably takes longer to work out what animal I’m thinking of!

So how do we build a good tree?

• Nice and even! (This is called a balanced tree)
• Every question splits the animals in half and rules out half the animals
• Gets to final animal faster

So how do we build a good tree??

Does it have hair/fur?

YES

NO

YES

Does it have legs ?

NO

Ask good questions, at the right time to halve the group

So how do we build a good tree??

Does it have hair/fur?

YES

NO

Repeat for each half!

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Now you’ve ruled some out maybe some different questions are useful.

Could you keep it as a pet?

YES

NO

So how do we build a good tree??

Does it have hair/fur?

YES

NO

Could you keep it as a pet?

YES

NO

Does it have feathers?

YES

NO

What are we going to do?

• Each team gets a pack of Celebrity Heads cards.
• There are cards with information about the characters.
• There are 2 packs to try

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• Your task is to look at the information on the cards and make a Celebrity Heads algorithm decision tree!

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How do we do it?

• Look at the information on the cards
• Start at the top and decide a question that will split the group of celebrities in half. The answer for the question is YES or NO
• Repeat for each of the halves you just made
• Gradually split it down until each group has only one left - write the character at the bottom of that branch

Remember - make a balanced tree!

• Ask good questions that will split the group in half
• Make your tree as flat and even as possible

How to play?

When you’ve finished building your Celebrity Heads algorithm decision tree …

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• Someone picks a card at random (don’t look at it!)
• If they want to, stick it to their forehead like in Celebrity Heads!
• That person asks your group the questions on your decision tree to work out which character they are
• Count how many questions they had to ask to work it out - the lower the better!

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You can call a tutor over to play your game!

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Let’s do it

• Get into groups of 3 - 5
• Each group gets:
• 1 sheet butchers paper
• Markers
• Student instruction sheet
• First card set
• Create your decision tree - write it on the paper
• Test it out then call a tutor over to play it

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• Grab the second (harder) card set and another sheet of paper
• Do it again!

Ask a tutor if you get stuck!