2. Starter Activity: Crossing Water
Open the ‘Crossing Water’ activity. It is in the
Getting Technical folder in Groupwork. ‘You need
to help the adults and children cross the water
but they can’t all go in the boat together.
Algorithms
3. In this lesson you will learn about algorithms and
how computers use them. You will write a simple
algorithm, perform a simple and selection sort
and determine which one is the most efficient.
Lesson
Objectives
Understand the purpose of an algorithm
Be able to create simple algorithms using English
Be able to complete simple and selection sorts
Be able to compare algorithms for efficiency
Algorithms
5. Algorithms
•An algorithm is a precise set of instructions for
completing a task
•Every time you follow a series of step by step
actions you are using an algorithm
•Starting a car, getting dressed, logging into your
computer are all completed using an algorithm
•Computers use algorithms that people have written
to solve all kinds of tasks for example to search for
documents or to sort your documents
Algorithms
6. Example Algorithm
Here is an algorithm for making a pot of tea:
1.If the kettle does not contain water then fill the kettle
2.Plug the kettle into the plug socket and turn on
3.If the teapot is not empty then empty teapot
4.Place tea bag in the teapot
5.If the water in the kettle is not boiling then go to step 5
6.Switch the kettle off
7.Pour water from the kettle into the teapot
Algorithms
7. Task 9: Ice Lolly Algorithm
Write an algorithm for making ice lollies out of
water and fruit cordial.
Algorithms
8. Simple Sort Algorithm
Watch the Simple Card Sort animation, this will
illustrate a simple sort algorithm.
Algorithms
9. Task 10: Simple Card Sort
1.You will be given a hand of unsorted cards
2.Repeat steps 3 through 5 until the unsorted hand
is empty
3.Compare unsorted cards
4.Select the smallest unsorted card
5.Move this card to the sorted hand
6.Stop
Algorithms
10. Computer - Simple Card Sort
Computers will carry out similar sorts but with
numbers rather than cards. The computer would
find the smallest number and then copy it to a new
list called an array. The original number would be
replaced with a special number called MAX. No
number can be greater than MAX. This process
would be repeated until all the numbers have been
considered and the array was sorted.
Algorithms
11. Selection Sort Algorithm
Watch the Selection Card Sort animation, this will
illustrate a selection sort algorithm.
Algorithms
12. Task 11: Selection Card Sort
1.You will be given a hand of unsorted cards
2.Use a pen to set a marker for the unsorted section at the front of
the hand
3.Repeat steps 4 through 7 until one card remains in the unsorted
section
4.Compare all unsorted cards
5.Select the smallest unsorted card
6.Swap this number with the first card in the unsorted section
7.Advance the marker to the right one card
8.Stop
Algorithms
13. Computer - Selection Sort
The computer would add a marker at the beginning
of the array of unsorted numbers. To sort the
numbers, the computer would repeatedly search
the unsorted section for the smallest number, swap
this number with the first number in the unsorted
section and advance the sort marker. This process
would be repeated until there was only one
number in the unsorted section. At this point the
list of numbers will be sorted.
Algorithms
14. Efficiency of Algorithms
The efficiently of algorithms can be measured by
calculating:
1.The amount of memory they use
2.The amount of copying, comparing and swapping
of numbers
Algorithms
15. Which Sort Algorithm is the Best?
1.As the selection sort swaps the numbers rather
than copying them into a new list it uses memory
than the simple sort.
2.Since the simple sort does not swap numbers it
would perform the least number of copies however,
it would perform twice as many comparisons as the
selection sort.
3.It is difficult to say which algorithm is the best as it
all depends on the original list, because of this
algorithms are measured on a worst case basis.
Algorithms
16. Task 12: Most Efficient Algorithm
Analyse the figures below to find out which sort is
the most efficient. The figures are all based on
worst case. Write-up your findings and justify your
decision.
Algorithms
No of Items Simple Selection
10 90 45
100 9,900 4,950
1000 999,000 499,500
10000 99,990,000 49,995,000
No of Items Simple Selection
10 10 27
100 100 297
1000 1,000 2,997
10000 10,000 29,997
Copies RequiredComparisons Required
17. Plenary: Alien Message
Write a short message to an alien explaining what
you have learnt in todays lesson. They only
understand basic English so think carefully about
the terminology you use.
Algorithms
18. Keywords
Understand the purpose of an algorithm
Be able to create simple algorithms using English
Be able to complete simple and selection sorts
Be able to compare algorithms for efficiency
Objectives
Algorithm
Instructions
Sort
Array
Marker
Memory
Simple
Selection
Algorithms
