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What's The Plan?Algorithmic Thinking

Step-by-step directions for whatever someone, or the

computer, needs to do

© 2004 Lawrence Snyder

FIT100FIT100Let’s Get Thinking.

• Activity: The Impossible Question In groups you will write out the instructions for how

to create a paper airplane. After you finish your instructions you will test them with another group. You will turn in: Instructions: Role Documentation: Test Results.

– FOUR ROLES» QUESTIONER: Write down all questions asked or problems posed

» ASSUMER: Write down all assumptions made.

» DOCUMENTER: Write down the algorithm.

» RESEARCHER: Gather information for your group

• Test Result Reflection: – Were all members of the group able to follow your

instructions– Did you have any unexpected results

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Instructions on how to build a paper airplane

FIT100FIT100Review: Paper Airplane

• Activity: Paper Airplane• How did the paper airplane activity

go?• What did you learn?• Are specific instructions easy to give?• Did you re-write your algorithm

between user tests?

FIT100FIT100Algorithm

• A precise, systematic method for producing a specified result

• In real life we do this all the time:

• What is a task that you complete daily where you do the same each time?

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Five Essential Properties of Algorithms

1. Input specified Data to be transformed during the

computation to produce the output Must specify type, amount, and form of

data

2. Output specified Data resulting from the computation—

intended result It is possible to have no output

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Five Essential Properties (cont'd)

3. Definiteness Specify the sequence of events Details of each step, including how to

handle errors

4. Effectiveness The operations are doable

5. Finiteness Must eventually stop

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FIT100FIT100Let’s Get Thinking

• Activity: Creating a plan In groups of 4 you will get an algorithmic

task. Some of these tasks were used as interview questions. We are concerned with the process you follow to arrive at your solution.

– FOUR ROLES» QUESTIONER: Write down all questions asked or

problems posed

» ASSUMER: Write down all assumptions made.

» DOCUMENTER: Write down the algorithm.

» RESEARCHER: Gather information for your group

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An Example: Directions

• What is an algorithm for getting to the closest McDonald’s? Input? Output? Definiteness? Effectiveness? Finiteness?

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FIT100FIT100WEATHER

WHETHER

FIT100FIT100Context Matters

• Program can fulfil five properties of an algorithm, be unambiguous, and still not work right because it is executed in the wrong context e.g., last name in Western countries means family

name; in Asian countries it may mean given name

• Context matters: Driving instructions "From the Bothel Everett Highway go to Starbucks

and turn right." Assumes you are traveling in a specific direction. If

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FIT100FIT100Language in Algorithms

• Natural language For people, we use a natural language

like English Ambiguity is common in natural

language

• Programming Language Formal languages designed to

express algorithms Precisely defined; no ambiguity

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FIT100FIT100Driving vs. Driverless

• http://www.youtube.com/watch?v=yDVLUiJfpPw

FIT100FIT100Program vs. Algorithm

• A program is an algorithm that has been customized to

solve a specific task

•under a specific set of circumstances

–using a specific language

• Algorithm is a general method; program is a specific method

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