solving programming problems

8/19/2019 Solving Programming Problems

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Solving ProgrammingProblems

A Seven-step Approach


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Solving Programming Problem

• Last lessons: Green screen example

• Specific problem that we wanted to solve

• Worked through step-by-step

• Problem statement! working code

• Now: A closer look at solving problems

• Seven step approach


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Solving Programming Problem

I want to be able totake a foreground

image and abackground image

and…

var fgImage = new SimpleImage("drewRobert.png");

var bgImage = new SimpleImage("dinos.png");var output = new SimpleImage(fgImage.getWidth(), fgImage.getHeight());for (var pixel of image.toArray()) { x = pixel.getX(); y = pixel.getY(); r = pixel.getRed(); g = pixel.getGreen();

b = pixel.getBlue(); if (g > r + b) { var pixel2 = bgImage.getPixel(x, y); output.setPixelAt(x, y, pixel2); } else {

output.setPixelAt(x, y, pixel); } }

print(output);

Problem Statement Working Code

Big Leap:

Break It Down


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Seven Steps

Work

Example ByHand

Write DownWhat You Did Find Patterns Check By

Hand

Translate ToCode

Run TestCases

Debug FailedTest Cases

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Step 1

• Solve small instance by hand

• Unclear problem?

• Need domain knowledge?

Work

Example ByHand

Write DownWhat You Did Find Patterns

Check ByHand

Translate ToCode

Run TestCases


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Step 2

• Write down exact steps

• Just that instance

• Tricky: do without thinking

Work

Example ByHand


Check ByHand

Translate ToCode

Run TestCases


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Step 3

• Algorithm for any instance

• Find patterns

• Repetition, conditions, values

Work

Example ByHand


Check ByHand

Translate ToCode

Run TestCases


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Step 3

• Difficulties?

• Try Step 1 + 2 again

• Different inputs

Work

Example ByHand


Check ByHand

Translate ToCode

Run TestCases


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Step 4

• Incorrect pattern? Find now

• Check with different inputs

Work

Example ByHand


Check By

Hand

Translate ToCode

Run TestCases


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Step 5

• Translate algorithm to code

• Programming language

Work

Example ByHand


Check By

Hand

Translate To

Code

Run TestCases


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Step 6

• Run test cases on code

• Execute program

• Check answer

Work

Example ByHand


Check By

Hand

Translate ToCode

Run TestCases


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Step 7

• Test failed? Debug

• Use scientific method

• Understand problem + fix

Work

Example ByHand


Check By

Hand

Translate ToCode

Run TestCases


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Step 7

• Algorithmic problem?

• Implementation problem?

Work

Example ByHand


Check By

Hand

Translate ToCode

Run TestCases


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Seven Steps

Work

Example ByHand


Check By

Hand

Translate ToCode

Run TestCases


1 2 3 4

5 6 7

solving programming problems

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