Lesson 2

GCSE Computing

StarterLook at the hand out you have been given.

Can you sort the numbers into ascending order.

What mental or physical methods did you use to sort them?

Algorithms - Sorting Sorting algorithms are very frequently used in programming. There are many situations in which data needs to be sorted. There are many different sorting algorithms out there that have

different level of efficiencies.

Some example of sorts: Bubble Selection Insertion Quick

VIDEO – Sorting.mp4

Algorithms - Sorting

Bubble SortAlgorithm for bubble sort

count1 = length of listcount2 = length of list -1FOR 1 to count1

FOR 1 to count2IF list[count2] > list[count2+1] THEN

temp = list[count2]list[count2] = list[count2+1]list[count2+1] = temp

ENDIFENDFOR

ENDFOR

Algorithms - Sorting

Bubble Sort6 2 1 3 2 1 4 0 1 3

2 6 1 3 2 1 4 0 1 3

2 1 6 3 2 1 4 0 1 3

2 1 3 6 2 1 4 0 1 3

2 1 3 2 6 1 4 0 1 3

2 1 3 2 1 6 4 0 1 3

2 1 3 2 1 4 6 0 1 3

2 1 3 2 1 4 0 6 1 3

2 1 3 2 1 4 0 1 6 3

2 1 3 2 1 4 0 1 3 6

Key

Sorted list

Items being swapped

Algorithms - Sorting

Bubble Sort

1 2 3 2 1 4 0 1 3 6 Key

Sorted list

Items being swapped

1 2 2 3 1 4 0 1 3 6

1 2 2 1 3 4 0 1 3 6

1 2 2 1 3 0 4 1 3 6

1 2 2 1 3 0 1 4 3 6

1 2 2 1 3 0 1 3 4 6

1 2 2 1 3 0 1 3 4 6

Etc.......

Using your numbers – use the bubble sort method to sort your numbers

Algorithms - Sorting

Selection sortAlgorithm for selection sort

minimum = 99999999count1 = length of listcount2 = length of listpositionofminimum = 1

FOR 1 to count1FOR 1 to count2

IF list(count2) < minimum THENminimum = list(count2)positionofminimum = count2

ENDIFENDFOR

temp = list(count1)list(count1) = list(positionofminimum)list(positionofminimum) = temp

END FOR

6 2 1 3 2 1 4 0 1 3Key

Sorted list

Items being swapped

0 2 1 3 2 1 4 6 1 3

0 1 2 3 2 1 4 6 1 3

0 1 1 3 2 2 4 6 1 3

0 1 1 1 2 2 4 6 3 3

0 1 1 1 2 2 4 6 3 3

0 1 1 1 2 2 4 6 3 3

0 1 1 1 2 2 3 6 4 3

0 1 1 1 2 2 3 3 4 6

0 1 1 1 2 2 3 3 4 6

Algorithms – SortingSelection

Using your numbers – use the selection sort method to sort your numbers

Algorithms – Sorting

Insertion Sort

Algorithm for insertion sort

FOR every item in listSort into new list by inserting it into correct place, one item at a time.

END FOR

Algorithms – Sorting

Insertion Sort

6 2 1 3 2 1 4 0 1 3

2 6 1 3 2 1 4 0 1 3

1 2 6 3 2 1 4 0 1 3

1 2 3 6 2 1 4 0 1 3

1 2 2 3 6 1 4 0 1 3

1 1 2 2 3 6 4 0 1 3

1 1 2 2 3 4 6 0 1 3

0 1 1 2 2 3 4 6 1 3

0 1 1 1 2 2 3 4 6 3

0 1 1 1 2 2 3 3 4 6

Key

Sorted list

Using your numbers – use the insertion sort method to sort your numbers

Algorithms - Sorting Look at these examples of how different algorithms can change

the speed of the sorting

Link 1 – CLICK HERE

http://www.sorting-algorithms.com/

Link 2 – CLICK HERE

http://www.cs.ubc.ca/~harrison/Java/sorting-demo.html

Algorithms - Sorting Task

With a bit of research – compare and contrast the bubble sort, insertion sort, selection sort and Quick sort.

Ask yourself the following questions

1) Can you describe how each one works?2) What is difference between them?3) Which one is the most efficient?4) Why do you think one is more efficient than another – what

makes is more efficient?