HCF and LCM algorithms

Posted on October 13, 2020 by Administrator Posted in Computer Science, Python - Intermediate, Python Challenges, Solved Challenges

In this Python challenge we will write two functions to calculate and return the Highest Common Factor (HCF) and the Lowest Common Multiple (LCM) of two numbers.

Highest Common Factor (HCF)

Note that the HCF is also known as the GCD (Greatest Common Divisor).

To calculate the HCF of two numbers we will write a function based on Euclid’s Division Algorithm. Your function called HCF() will take two parameters and will be based on the following flowchart:

Python Code

Create the HCF() function on the Python trinket below:

Lowest Common Multiple

Once we have worked out the HCF of two numbers we can easily calculate their Lowest Common Multiple (LCM). The LCM of two numbers a and b is their product divided by their HCF:

LCM(a, b) = ab/HCF(a,b)

Your task is to create a new Python function called LCM() that takes two parameters a and b and returns the LCM of the two numbers using the above formula.

Test Plan

Use the following test plan to test both the HCF() and LCM() functions.

Test #	Input Values	Expected Output	Actual Output
#1	a: 32 b: 24	HCF: 8 LCM: 96
#2	a: 45 b: 30	HCF: 15 LCM: 90
#3	a: 78 b: 24	HCF: 6 LCM: 312
#4	a: 60 b: 20	HCF: 20 LCM: 60
#5	a: 100 b: 21	HCF: 1 LCM: 2100
#6	a: 96 b: 72	HCF: 24 LCM: 288

Solution...

The solution for this challenge is available to full members!
Find out how to become a member:
➤ Members' Area

Euclid’s Division Algorithm

Posted on October 13, 2020 by Administrator Posted in Computer Science, Computing Concepts, Python - Intermediate, Python Challenges

Euclid’s division algorithm is used to calculate the Highest Common Factor (HCF) of two positive numbers. It is based on Euclid’s division lemma and can be implemented in just a few lines of high level code. You can read more about this algorithm on this page.

Euclid’s Division Algorithm: Pseudocode

INPUT a #The largest of two numbers
INPUT b #The smallest of two numbers
WHILE b > 0
   temp = b
   b = a MOD b
   a = temp
END WHILE
OUTPUT a

Trace Table

Do get a better understanding of how this algorithm works we will complete the following trace tables assuming that the two input values a and b will be a = 32 and b = 24. The output (Highest Common Factor) of this program should be 8.

Complete the trace table below to find out if this algorithm will produce the required output.

Line Number	a	b	b > 0?
1	32
2		24
3			True
…

Python Code

You can now create a function called calculateHCF() that takes two parameters, a and b and returns the HCF of these two numbers using Euclid’s division algorithm.

To improve your code, you should make it work even when number b is greater than number a.

Test Plan

Test your function using the following test plan:

Test #	Input Values	Expected Output	Actual Output
#1	a: 32 b: 24	8
#2	a: 45 b: 30	15
#3	a: 78 b: 24	6
#4	a: 60 b: 20	20
#5	a: 100 b: 21	1
#6	a: 96 b: 72	24
#7	a: 72 b: 96	24

Tagged with: Trace Table

Input, Output & Storage Devices: Quiz!

Posted on October 7, 2020 by Administrator Posted in Computer Hardware, Computer Science, Computing Concepts, Computing Terminology Quiz, GCSE Concepts, Quizzes

Computers hardware consists of all the components that you will find inside the computer (Motherboard, CPU, RAM, graphic card, sound card, network card, etc.) as well as all the peripherals/devices than you can plug to a computer.

Peripherals are often categorised into three types:

Input Devices,
Output Devices,
Storage Devices.

Input Devices	Output Devices	Storage Devices
Mouse Keyboard Microphone Webcam Scanner Barcode Reader Sensors Chip & Pin Card Reader Magnetic Stripe Card Reader Touchpad Game Controller Joystick	Screen/Monitor Projector Speakers Headphones Printer (Inkjet or Laserjet) 3D Printer Actuators LED	Magnetic Hard drive SSD Hard drive USB Key CD Drive DVD Drive Bluray Disc/Drive SD Card Reader

Take the Quiz! (open full screen)

ASCII Quiz Challenge

Posted on August 27, 2020 by Administrator Posted in A Level Concepts, Computer Science, Computing Concepts, GCSE Concepts, Python - Intermediate, Python Challenges, Solved Challenges

ASCII Code

The ASCII code (Pronounced ask-ee) is a code for representing English characters as numbers, with each character assigned a number from 0 to 127. For example, the ASCII code for uppercase A is 65. The extended ASCII contains 256 characters (using numbers from 0 to 255).

To see a list of the most useful ASCII codes, you can download our simplified ASCII helpsheet.

Each character that appears on your keyboard has a unique value. This includes the 26 lowercase letters & 26 uppercase letters of the alphabet, the number digits from 0 to 9 and a range of punctuation signs and special characters.

Take the Quiz! (open full screen)

chr() and ord() functions

Using Python, you can easily access ASCII values of a character using the ord() function. And vice-versa, the chr() function is used to retrieve the character matching a given ASCII value. For instance:

ord(“A”) returns 65
chr(65) returns “A”

ASCII Quiz in Python

Your Python challenge consists of recreating the above game where the user tries to guess the ASCII value of different characters randomly selected. The difference between the user’s guess and the actual ASCII value of the character being displayed is used to decrement a life score.

The user starts the game with a life score of 255 and tries to guess as many ASCII values as possible before reaching a life score of 0. Any correct answer (exact ASCII value guessed) automatically resets the user’s life score to 255!

Solution...

The solution for this challenge is available to full members!
Find out how to become a member:
➤ Members' Area

Prolog – Food Web Challenge

Posted on July 10, 2020 by Administrator Posted in A Level Concepts, Computer Science, Computing Concepts

Prolog is a language built around the Logical Paradigm: a declarative approach to problem-solving.

There are only three basic constructs in Prolog: facts, rules, and queries.

A collection of facts and rules is called a knowledge base (or a database) and Prolog programming is all about writing knowledge bases. That is, Prolog programs simply are knowledge bases, collections of facts and rules which describe some collection of relationships that we find interesting.

So how do we use a Prolog program? By posing queries. That is, by asking questions about the information stored in the knowledge base. The computer will automatically find the answer (either True or False) to our queries.

Source: http://www.learnprolognow.org/

Knowledge Base (Facts & Rules)

Check the following knowledge base used to store the information that appears on a food web:

/* Facts */
plant(grass).
plant(berries).
plant(nuts).

insect(caterpillar).
insect(butterfly).

animal(squirrel).
animal(goldfinch).
animal(fox).
animal(snake).
animal(frog).
animal(eagle).
animal(X) :- insect(X).

insectivore(frog).
insectivore(goldfinch).  

eats(caterpillar,grass).
eats(butterfly,berries).
eats(goldfinch,berries).
eats(squirrel,nuts).
eats(fox,squirrel).
eats(fox,goldfinch).
eats(snake,goldfinch).
eats(snake,frog).
eats(eagle,frog).
eats(eagle,snake).
eats(eagle,goldfinch).
eats(X,Y) :- insectivore(X), insect(Y).         

/* Rules */
herbivore(X):- eats(X,Y), plant(Y).
carnivore(X):- eats(X,Y), animal(Y).
omnivore(X):- herbivore(X), carnivore(X).

predator(X,Y):- eats(X,Y).
prey(X,Y):- eats(Y,X).

pyramid(X,Y):- prey(Y,X).
pyramid(X,Y):- prey(Z,X), pyramid(Z,Y).

Queries

We can now query this database. For each of the queries listed below, what do you think the computer will return?

True or False Queries:
The following queries would return either True or False.

?-herbivore(butterfly).
?-herbivore(fox).
?-omnivore(goldfinch).
?-predator(fox,squirrel)
etc.

Other Queries:
The following queries would return a solution which could be either:

A unique value
A list of values
False if no solution can be found

?-animal(X)
?-herbivore(X).
?-predator(goldfinch,X).
?-pyramid(fox).
etc.

Your Task:

Use a range of queries, similar to the one above to interrogate the knowledge base and complete the food web provided below.

To run your queries you will need to use the online Prolog environment:
https://swish.swi-prolog.org/p/Food-Web-Prolog.pl

Here is the template for the food web for you to complete:

Tagged with: Prolog

Logic Gates Diagrams (Whiteboard)

Posted on June 26, 2020 by Administrator Posted in A Level Concepts, A Level Quiz, Computer Hardware, Computer Science, Computing Concepts, GCSE Concepts, GCSE Quiz, Quizzes

QuestionAnswer

Draw the logic gates diagram for the following Boolean expression:

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Scratch – Sprite Movement using a Touchscreen

Posted on June 15, 2020 by Administrator Posted in Block Programming, Scratch

Many tutorials on how to create a game in Scratch will be based on using the arrow keys to control the main sprite. This is a great approach indeed but is not suitable if you are designing the game toe be used on a tablet or smartphone. In this case, your input device to control the main sprite is not the keyboard but the touchscreen.

The following short tutorial will show you how you can control the movement of your sprite (in this case the cat) using a touchscreen. The idea will be to create two other sprites/buttons called Arrow_Left and Arrow_Right that, when clicked using a mouse or tapped using a touchscreen will tell the cat sprite to move in the relevant direction.

You can recreate this code online using the scratch website.

Step 1: Right ArrowStep 2: Left ArrowStep 3: Main SpriteStep 4: Up & Down

Step 1: Arrow_Right Sprite

You will need tot create a new sprite and use the arrow sprite from the scratch library.
scratch_arrow_sprite

You should rename this sprite “Arrow_Right”.

You will then need to add the following code to this sprite to detect when the user clicks or taps on this sprite:

Step 2: The Arrow Left

Repeat the instructions from Step 1 to create another arrow sprite and call it “Arrow_Left”. The code for this new sprite will be as follows:

You will also need to change the costume of this sprite to show an arrow pointing to the left:

The main sprite (in this case the cat, will need to move left or right when it receives the messages “left” and “right”. To do so we will use the following code (on the cat sprite):

You can repeat the above steps to create an Arrow_Up and a Arrow_Down sprite if it is relevant to your game.

Thank You Medical Staff and Key Workers!

Posted on May 7, 2020 by Administrator Posted in Computer Science, Python - Beginner, Python Challenges, Solved Challenges

During the coronavirus pandemic, the rainbow has become a symbol of gratitude for the medical staff working in hospitals as well as all the other key workers who carried on working to provide essential services to their community.

All over the UK, children have drawn or painted colourful rainbows and have displayed them on their windows or front doors.

In this challenge, we will use some python code to draw a rainbow and a “Thank You” message to all medical staff and key workers.

This is what the output of our code should look like:

Your Task

We have written the code using Python Turtle but it does not produce the expected outcome.

Could you:

Change lines 20 to 28 to make sure the code displays the colours of the rainbow in the right order
Change lines 30 to 35 to make sure the stars and text are of the right colours.

The output of your code should be the same as the above picture.

Extension Task

You can tweak this code further to change the message or improve the overall look and feel further for instance by adding more stars and playing with the colours used to display the text.

Solution...

The solution for this challenge is available to full members!
Find out how to become a member:
➤ Members' Area

Tagged with: Python Turtle, Sequencing

Colour Luminance and Contrast Ratio

Posted on April 28, 2020 by Administrator Posted in Computer Science, Python - Intermediate, Python Challenges

The luminance of a colour is a measure used to describe the perceived brightness of a colour. It is possible to calculate the luminance of a colour based on its RGB colour code.

So let’s consider an algorithm that collects an RGB colour code as an input, using the (255,255,255) format. The algorithm will then convert these R, G, B values to a 0 to 1 scale as follows:

New R₁,G₁ B₁ values are then calculated using the following rules:

Finally, the luminance value of the colour can be calculated using the following formula:

The reason such complex formulas are necessary to calculate the luminance (“perceived brightness”) of a colour is partly because our eyes’ perception of the brightness of a colour is not linear (it is not directly proportionate to the number of photons being emitted by a computer screen). Effectively our eyes perceive more levels of light in dim conditions, and less in brighter conditions.

Luminance Function

Your first task is to write a function called luminance() that takes 3 parameters r, g and b corresponding to the RGB values of a colour (integer values between 0 and 255). Your function will use the above algorithm to calculate and return the luminance of the given colour.

You can use the trinket at the bottom of this page to write the Python code for this fucntion.

Contrast Ratio

The contrast ratio defines how easy a human eye recognises text or images on a coloured background.

The contrast ratio is a numerical ratio between 1:1 and 21:1.
To be easily readable, the contrast ratio between the text colour and the background colour must be at least 7:1.
A contrast ratio of at least 4.5 may suffice for larger text.

To calculate the contrast ratio between two colours (e.g. font/text colour and background colour) you must first calculate the luminance of both colours and identify which colour is the lightest colour and which colour is the darkest colour. You can then use these luminance values (labelled L_light and L_dark) to calculate the contrast ratio as follows:

Contrast Ratio Function

Your second task is to write a function called contrastRatio() that takes 6 parameters corresponding to the RGB values of two colours (integer values between 0 and 255). Your function will work out the luminance values of both colours, identify the lightest of the two colours and use the above formula to calculate and return the contrast ratio between these two colours.

Test Plan

Once your code is complete, check that it works as expected using the following four tests:

Test #	Input Values	Expected Output	Pass/Fail?
#1	(255,255,255) (0,0,0)	Luminance: 100% Luminance: 0% Contrast Ratio: 21
#2	(148, 57, 173) (174, 84, 199)	Luminance: 12.24% Luminance: 19.46% Contrast Ratio: 1.42
#3	(148, 57, 173) (209, 157, 223)	Luminance: 12.24% Luminance: 43% Contrast Ratio: 2.78
#4	(148, 57, 173) (245, 232, 248)	Luminance: 12.24% Luminance: 83.9% Contrast Ratio: 5.16

Magic Trick Algorithm

Posted on April 24, 2020 by Administrator Posted in Algorithms, Algorithms (GCSE), Computer Science, Computing Concepts, GCSE Concepts

In this blog post we are investigating whether we can teach a computer how to perform a magic trick.

Algorithm

If you want a computer to perform a specific task you need to provide this computer with a clear set of instructions that the computer will repeat, one instruction at a time. We call such a set of specific instructions an algorithm.

One of the key characteristic of an algorithm is that the instructions are given in a specific order, forming a sequence of instructions. When the computer will complete your algorithm, it will complete each instructions one instruction at a time in the order they appear on the algorithm. We call this sequencing, a key concept of computer algorithms.

When designing an algorithm, we can either write our instructions as a list (Pseudocode) or we can use a more visual representation of our algorithm using a flowchart.

Magic Trick Algorithm

We have implemented a magic trick algorithm based on a small deck of cards. When you press the start button below, the computer will follow the sequence of instructions from this algorithm to perform the magic trick.

Let’s see if the computer can perform this magic trick successfully:

Click on the button below to start the magic trick!

Magic Trick Algorithm/Flowchart

The flowchart for this algorithm will help you work out how the actual card trick works!

Click on the above flowchart to open in a new window.

Tagged with: Sequencing

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Highest Common Factor (HCF)

Python Code

Lowest Common Multiple

Test Plan

Solution...

Euclid’s Division Algorithm: Pseudocode

Trace Table

Python Code

Test Plan

Take the Quiz! (open full screen)

ASCII Code

Take the Quiz! (open full screen)

chr() and ord() functions

ASCII Quiz in Python

Solution...

Knowledge Base (Facts & Rules)

Queries

Your Task:

Step 1: Arrow_Right Sprite

Step 2: The Arrow Left

Your Task

Extension Task

Solution...

Luminance Function

Contrast Ratio

Contrast Ratio Function

Test Plan

Algorithm

Magic Trick Algorithm

Magic Trick Algorithm/Flowchart

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