91074 – Algorithm Languages and User InterfacesSorting: Bubble Sort, Selection Sort, Insertion Sort, Quick Sort. Comparisons, Cost of an Algorithm.
Contents•Sorting Algorithms
• Informal Instructions, Algorithms and Programs
•High and Low Level Languages
•Translating Between Languages
•User Interfaces
Sorting AlgorithmsSorting: Bubble Sort, Selection Sort, Insertion Sort, Quick Sort. Comparisons, Cost of an Algorithm.
Activity1) In groups, sort a small number of cards numerically2) What was your algorithm/strategy?
– tell your group.
3) New Rules: only allowed to look at two cards at a time, only allowed to swap two, no other moves.
4) What was your algorithm/strategy?
NotesSorting Algorithms: There are lots of ways computers sort lists. In this course we will look at Bubble sort, Selection Sort, Insertion Sort and Quick Sort.
Cost of an Algorithm: For sorting giant lists (like a phone book) on a computer, speed is important. We call this the ‘cost of the algorithm’ and we measure it by how many comparisons the algorithm has to make for a set list size.
Bubble Sort Instructions1) Compare the first two2) If out of order swap them3) Look at the next two, 4) Repeat Steps 2 and 3 until the (new) end of
the list.5) Repeat steps 1 – 4 until the list is sorted
Called Bubble Sort because like bubbles in a glass, the next one makes it way to the top
Bubble Sort Cost
E4E: Formula?
List size Comparisons required
5 10
6
7
8
10
Example Bubble Sort Video
Bubble Sort and Cost Video (sorting by height)youtube.com/watch?v=cdsfjU8qUss
Selection Sort1) Compare the first two and find the biggest2) Then compare the biggest with the next one3) Remember which is the (new) biggest4) Repeat steps 2 and 3 until the end5) Swap the biggest one with the (new) last one6) Repeat steps 1 to 5 until the list sorted
Called Selection, because you are selecting the biggest one and swapping it to the end.
Selection Sort Cost
E4E: Formula?
List size Comparisons required
5 10
6
7
8
10
Insertion Sort1) Compare the first two, and put them in order in a
new list2) Insert the next item into the right place in the new
list by comparing it with each item until you find it’s place.
3) Repeat step 2 until the new list is sorted, and the old list is empty.
Called Insertion, because you’re inserting into the correct position in a new list.
Insertion Sort Cost
E4E: Formula?
List size Comparisons required
5
6
7
8
10
Quick Sort (pivot)1) Select the next (first) item and make it a pivot2) Compare each item with the pivot, creating a list of
smaller items and a list of bigger items. 3) Repeat steps 1 and 2 for each sublist, until the list is
sorted
Is one of a group of “divide and conquer” sorting algorithms
Called Pivot, because you separate the list into smaller lists based on a pivot.
‘Pivot’, Friends on Youtube
Quick Sort Cost
E4E4E: Formula?
List size Comparisons required
5
6
7
8
10
Some ComparisonsWhich one is fastest, which is second fastest?
Sorting lists of 20Bubble Selection Insertion Quick
Click to see them race
Some ComparisonsWhich one is fastest, which is second fastest?
Sorting lists of 20Bubble Selection Insertion Quick
Some ComparisonsBubble Sort vs Quick Sort (Youtube) Lists of 30 coloured blocks, Comparing swaps, not Comparisons
1) Which has the least comparisons?2) Which has the least swaps?3) Is comparisons or swaps the best way to measure
“Cost of Algorithm?”
Comparing Sorting Comparisons
Watch Pivot Video (youtube)
List size (n)
BubbleComparisons
Selection Comparisons
InsertionComparisons
QuickComparisons
5 10 10 9~ 8~6 15 15 12.5~ 11~7 21 21 16.5~ 13~
10 45 45 31.5~ 25~20 190 190 114~ 63~
100 4950 4950 2574~ 500~Formula ½(n2 – n) ½n2 – ½n ¼n2 +¾n –1
(Average)n ln n
(Average)
Practice Task
Part A) Pick a sort, and six items. Step by step talk through sorting six items. E.g Carrot, Apple, Grape, Banana, Eggplant, Feijoa, - compare Carrot and Apple. (Out of order, so swap)- Compare Carrot and Grape (in order)- Compare Grape and …Part B) Do an insertion sort for 5, 6, 7 and 8 items, recording the cost.Part C) Explain how you calculated the cost and say why that is the cost.
Links
Getting sort data quicklyhttp://www.mundayweb.com/progs/applets/saas/Or search “Munday Saas”
Running your own raceshttp://www.sorting-algorithms.com/ Has eight common sorts
Informal Instructions Algorithms and ProgramsTheir Characteristics and Roles
Algorithm Notes
▫An algorithm is a precise unambiguous specification of how to accomplish some computational task in a finite number of well-defined steps.
▫An algorithm is distinct from a computer program.
▫An algorithm has a cost (the number of steps it will perform) for a task.
▫Different algorithms for the same task may have different costs.
Informal Instructions, Algorithms and Programs
Youtube Video (Eating a Chocolate)youtube.com/watch?v=cdsfjU8qUss
Friendship Algorithm
Characteristics of Informal Instructions, Algorithms, & Programs
Informal Instructions: Vague, Imprecise, easy to read/create, interpreted many waysMay have: gaps, bad spelling, incompleteForm: oral or written,
Algorithms: Precise, single task, has inputs/outputs, made up of steps, has a cost, Form: code, flow chart, text
Programs: Many tasks, made up of algorithms, single file, precise, self running, many tasksForm: file
When are they used (Roles)Informal Instructions, Algorithms, & Programs
Informal Instructions: Humans, communication, ease,
Algorithms: code, computer, part /functions in prog,
Programs: a variety of functions, self contained
Programming Concepts
Informal Instructions:
Algorithms:
Programs:
High and Low Level LanguagesCharacteristics
High and Low Level Languages Video
Youtube Video (Eating a Chocolate)youtube.com/watch?v=cdsfjU8qUss
Low Level Languages Machine Code (1GL)
•1st Generation Language (1GL)•Numbering system called “Binary”•Also called “Machine Code”•The only way to Program computers in
the 1960s and 70s•Old Explanation of Binary (before 3GL)Binary total 8s
column4s
column2s
column1s
column
2 0 0 1 0
7 0 1 1 1
Low Level Languages Machine Code (1GL)
Binary GameBinary total 8s
column4s
column2s
column1s
column
3 0 0 1 15 0 1 0 1
13 1 1 0 17 0 1 1 1
Low Level Languages Machine Code (1GL)
Flight of the Conchords•Binary Solo
Big Bang Theory•Chuck Norris of Numbers•Palindrome = Reverse ,
1001001 1001001
Low Level Languages Machine Code (1GL)
Characteristics• Lowest Level Language•Very Hard for humans to understand•Very slow to create code•No abstraction: Human knows exactly
what’s going on•Directly interacting with hardware•Doesn’t need translating or compiling•Native Language of Computer
Low Level Languages Assembly (2GL)
Low Level Languages Assembly (2GL)
• 2nd Generation Language (2GL)•One step up from Binary/Machine code• Has functions like Move (MOV), Compare
(CMP), Increment (INC), Jump(JMP) •Uses Hexadecimal (like web colours #ffffff )• Has no Compound functions like “If (this,
then do this)” or “Loop (3 times)”• At the end it is “Assembled” into Binary•Used when you need exact control over
code (e.g very small microchip, efficient code needed)
Low Level Languages Assembly (2GL)
Assembler ExampleHello WorldIgnore music and second half
“The main problem with “assembler” jokes is, they are difficult to read”— scapegrace
Low Level Languages Assembly (2GL)
Characteristics•Second Lowest Level Language•Hard for humans to understand•Slow to create code• Little abstraction: Human knows
almost exactly what’s going on•Needs Assembling into Binary /
Machine Code / 1GL translating or
High Level Languages (3GL)
Common Programming LanguagesLike Basic, C, Java, C# and Scratch
High Level Languages (3GL)
Features•Easier to Read and Write (and maintain)•Portable across different CPU families•Written as Text•Many High Level Languages, each with
their own Syntax
High Level Languages (3GL)
Brief History of 3GLs
•1957 Fortran (punch cards)
•1964 Basic MS Visual Basic
•1972 C (text colouring) C++
•1995 Java (Object Oriented)
•2001 C# (OO, components)
•2007 Scratch (Drag n Drop)
High Level Languages (3GL)
Characteristics•High Level Language• Lots of Abstraction into easily
readable code•Easy for humans to understand•Quick to create code•Needs Translating
into Machine code
HighLevel Languages (4GL)
Lots of Abstraction
High Level Languages (4GL)
Features•Flow charts and
modules
•4GL creates the code for you
•Often for a specific task e.g Managing a tax database
High Level Languages (4GL)
Characteristics• Examples: Ruby on Rails, Oracle, Powerbuilder • High Level Language • Lots of Abstraction sometimes
not even looking at code • Very Quick to create code•Needs Translating
into Machine code
“All 4GLs are designed to reduce programming effort, the time it takes to develop software, and the cost of software development. They are not always successful in this task, sometimes resulting
in inelegant and unmaintainable code.” (wikipedia)
Comparison of Language Levels1 GL 2 GL 3 GL 4 GL
Level Low Low High High
Example Language(s) Machine Code Assembler C, Java,
Scratch…Oracle,
PowerBuilder…
Write in Binary (1, 0) Hexadecimal, and Text Text Text, Diagrams
Abstraction None A little Lots Lots
Ease of Code Creation Very Difficult Difficult Easy Very Easy
Speed of Code Creation Very slow Slow Fast Very Fast
Control over Machine Code
Full Precise control
Full Precise control Some control No control
Inelegant Code
Portability None Same family of CPUs
Completely Portable
Completely Portable
Challenge Question
Low and High Levels
Invention of High Level Languages (3GL)High Level and Translators- 1983 Educational Cartoon
BASIC C Java
Translating between High and Low Level LanguagesCompilers, and Interpreters
Translating (Compiling) VideoYoutube Video (Eating a Chocolate)youtube.com/watch?v=cdsfjU8qUss
Translating between Levels
Why do we need to Translate high level languages into low ones? - Because Binary is the only language
the computer understands- Creates precise code rather than abstract- So code is portable
Translating between Levels
Interpreters and Compilerson Planet Gooble De Gook- Made in 1983
Two types of Translator 1) Compilers
Do the whole program at once at the endCan save program down as an .exe file
2) InterpretersTranslate the whole program one line at a timeCan cause errors or refuse to run
User InterfacesHeuristics
User Interface VideoYoutube Video (Box Crusher)youtube.com/watch?v=cdsfjU8qUss
Mr Bell’s New Home Nightmare
Accidentally open Garage door
Mr Bell’s New Home Nightmare
Door bell is locked behind front door
User Interfaces
We measure the usability of a user interface through a series of tests called “Heuristics”.
What is a User Interface?/ What is a User Interface’s role?- Communication between user and computer/machine- Makes the program do what user wants it to- Inputs like, Button, key, wheel, mouse, handle, Switch, - Outputs like, lights, sound, speakers, visual, screen,
heat, display- Manages/ Controls interactions
Heuristics (tests for User Interfaces)
1. Visibility of system status 2. Match between system and the real world 3. User control and freedom 4. Consistency and standards 5. Error prevention 6. Recognition rather than recall 7. Flexibility and efficiency of use 8. Aesthetic and minimalist design 9. Help users recognize, diagnose, and recover from
errors 10. Help and documentation Look these up online – Jakob Neilsen made them up.
User Interfaces
50 different things that have a user interfacePlaystation, Door, Computer, Toaster, Phone, Drill, Bike, Car, Clock, Gun, Printer, Office Chair, Distortion pedal, Ipod, TV, Stereo, Projector, Websites, lightbulb, Scissors, Pen, Power Plug, Window, Air Conditioning, Curtain, Fridge, Stove, Watch, Jacket zip, car jack, shoe, toilet, shower, cap, tap, tack, cat door, badge, earring, glasses, Potato peeler, Cheese Grater, knitting needles, sewing machine, watter bottle, knife, vhs, can opener, Milk bottle, Towel, chop sticks, light, calculator, filing cabinet, Microwave, elevator, .
User Interfaces
Broadly Different Example User Interfaces- Microwave, Computer, TV, Door, Switch, Playstation, Scissors, Pen, Tissues, Toothpaste, phone, ipod, draw, Lever, Shoes, stereo, socks, pants, plug, pin, clock, projector, printer, Light bulb, toilet, sink, tap, shower, bath, car, shovel, rifle, wrench, digger, back pack, fork, remote control car, shopping trolley, DVD, book, pram, finger nail clippers, curtains, some geeky thing, mouse, bike pump, Hospital beds, jet pack, balloon, envelope, aeroplane, boat, rubbish bin, umbrella, chocolate bar (in wrapper) fishing rod, pizza box, kayak, kite, drink bottle, map, bow and arrow, charger, calculator, website.