Introduction

COMPSCI 105 SS 2015Principles of Computer Science

COMPSCI 1052

Lecturers Lecturers

Angela Chang (Course coordinator) Email: angela@cs.auckland.ac.nz Phone: 3737599 ext 86620 Room: 303S.585 Office hours: Tue, Wed, Thurs 11am-12noon

Or whenever the office door is open

Dr Mike Barley Email: barley@cs.auckland.ac.nz Phone: 3737599 ext 86133 Room: 303S.394 Office hours: TBA

Lecture 01

• Teaching Assistants• Steven Hu• qhu009@aucklanduni.ac.nz

• Monica Bian• rbia002@aucklanduni.ac.nz

COMPSCI 1053

Topics Making informed choices about programming

Understanding the trade-offs

Focus on ways of storing and manipulating data Different ways of structuring data storage Efficiency Searching Sorting

Some new programming ideas Importance of Abstraction Recursion, regular expressions, exceptions, data

interchange

Lecture 01

COMPSCI 1054

Assessment Note: Students must obtain a pass in both the

practical (assignments) and non-practical work (test + exam) in order to pass as a whole

Laboratories every week (starting next week) ………. 25% Pre-lab exercises & two laboratories per week

dues on every Thursday OR Saturday Note: labs to be submitted using CodeRunner 5 Pre-lab exercises (7%) 9 Laboratories (18%)

Mid-semester Test …………………………………... 10% Thurs 29th Jan, 10:00am – 11:00 am

Final Exam ………………………………………….. 65% Date to be announced

Lecture 01

COMPSCI 1055

Laboratories All Laboratories will be started from Monday 12 Jan. Two Laboratories per week

First Lab (Lab)/ Venue: G75 Streams:

Monday 12:00noon – 1:00pm Monday 1:00pm-2:00pm Tuesday 12:00noon – 1:00pm Tuesday 1:00pm-2:00pm Tuesday 2:00pm-3:00pm

Second Lab (Tut)/ Venue: B75 Streams:

Thursday 12:00noon – 1:00pm Thursday 1:00pm-2:00pm Thursday 2:00pm-3:00pm Friday 12:00noon – 1:00pm Friday 1:00pm-2:00pm

Lecture 01

COMPSCI 1056

Resources Lectures

Overheads and recordings Forum

Question and answers – peers, tutors and lecturers  http://forums.cs.auckland.ac.nz/

Textbook Problem Solving with Algorithms and Data Structures Online, free, open source

Additional resources Python.org PythonTutor.com

Lecture 01

COMPSCI 1057

CalendarWk Mo Tu We Th Fr

1

6/JanIntro, Python lists,List Comprehension

7Mutable objectsReferences and Equality

8Classes 1

9Classes 2

2

12Exceptions

13Exceptions 2

14JSON

15Algorithm Analysis

16Abstract Data Types, Stack ADT

3

19Stacks

20Queues

21Lists

22Lists 2

23Recursion 1 

4

26PUBLIC HOLIDAY

27Recursion 2

28Searching 

29TERM TEST

30Hash functions

52 Hash functions

3Sorting: Simple Sorts

4Sorting: Better Sorts

5Introduction to Trees

6PUBLIC HOLIDAY

6

9Priority Queues and Binary Heaps

10Using Trees - Expressions

11Binary Search Trees

12Binary Search Trees and RegularExpressions

13More Regular Expressions

Lecture 01

COMPSCI 1058

LaboratoriesWk Mo Tu We Th Fr

1

6 Jan 7 8 9

2

12Lab1

13Lab1

14 15Lab2

16Lab2

3

19Lab3

20Lab3

21 22Lab4

23Lab4

4

26PUBLIC HOLIDAY

27 28 29Lab5

30Lab5

5

2 FebLab6

3Lab6

4Lab7

5Lab7

6PUBLIC HOLIDAY

6

9Lab8

10Lab8

11 12Lab9

13Lab9

Lecture 01

COMPSCI 1059

AssessmentsWk Mo Tu We Th Fr Sat

1

6 Jan 7 8 9 10

2

12Due: prelab1 (1%)

13 14Due: Lab1 (2%)

15 16 17Due: Lab2 (2%)

3

19Due: prelab2 (1.5%)

20 21Due: Lab3 (2%)

22 23 24Due: Lab4 (2%)

4

26PUBLIC HOLIDAY

27Due: prelab3 1.5%)

28 29TERM TEST

30 31Due: Lab5 (2%)

5

2 FebDue: prelab4 1.5%)

3 4Due: Lab6 (2%)

5 6PUBLIC HOLIDAY

7Due: Lab7 (2%)

6

9Due: prelab5 1.5%)

10 11Due: Lab8 (2%)

12 13 14Due: Lab9 (2%)

Lecture 01

COMPSCI 10510

Class Representative Must elect a class rep Attends 2 staff student meetings Pass on student concerns to lecturers

Lecture 01

COMPSCI 10511

Revision – Python ProgramsWhen the steps in a process are well defined, we can store them in the computers memory in a way that the computer can follow them. The language we store the instructions must be

formal language Reduces ambiguity

Python is a programming language designed to be easy to read Each step in the program is known as a statement A program is a sequence of statements

Ways of running a program Interactive execution – great for learning Creating a module (file) and executing the module

Lecture 01

COMPSCI 10512

Variables Variables store information

Information is divided into different types Python is dynamically typed Variables do not need to be declared before they are

used Basic types

int, float, boolean, stringx = 34x = 34.5x = Truex = 'Hello'

Lecture 01

COMPSCI 10513

Tracing code Keep track of the contents of variables

Write down the name of each variable Change the value when (and only when) an

assignment occurs When you change a value, cross out the old one and

write a new one

length_in_inches: 50 100length_in_cms: 254.0

Lecture 01

COMPSCI 10514

Example 1 What is the output of the following code?

Perform a code trace.

a = 7b = 3c = 2d = 4e = a

a = bb = ee = cc = dd = eprint(a, b, c, d, e)

a

b

c

d

e

7

3

2

4

7

3

2

2

7

4

Lecture 01

Example01.py

COMPSCI 10516

Expression An expression is part of the program that can be

evaluated (i.e. when the computer follows the rules that define the instructions, an expression turns into a value).

An expression can be used anywhere that a value is used

x = 3 + 4

3 + 4 is an expression

Lecture 01

COMPSCI 10517

Example Floor division and modulus

Integer part of a division, and remainder after division

What do each of the following expressions evaluate to? 10 + 4 10 - 4 10 * 4 10 / 4 10 ** 4 10 // 4 10 % 4

14

6

40

2.5

10000

2

2

Lecture 01

Example01.py

COMPSCI 10518

Functions A function is a sequence of instructions designed

to perform a task, and is packaged as a unit. Functions have a name Functions accept arguments Functions return values

Syntax Indentation rather than braces are used to signify

blocks of code Variables defined within the scope of a function are

not available outside the function

def rectangle_area(width, height): return width * height

Lecture 01

COMPSCI 10519

Exercise 2 Write a function that calculates the area of a

circle area = π r2

Lecture 01

COMPSCI 10520

Boolean values and related operators Boolean values

True False

Relational operators >, >=, <, <=, ==

Boolean operators and, or, not

>>> 2 == 3

Lecture 01

False

True>>> 2 == 3 or 4 < 5

COMPSCI 10521

Conditionals Code is executed if the condition is true

if n < 0: print("Negative number")elif n > 0: print("Positive number")else: print("Zero")

if name == "Andrew": print("Hi Andrew")

if n % 2 == 0: print("Even number")else: print("Odd number")

Lecture 01

name

Andrew

n 6Hi Andrew

Even number

Positive number

COMPSCI 10522

Sequences Sequences allow you to store values in an

organized fashion. strings, lists, tuples, dictionaries, and sets http://en.wikibooks.org/wiki/Python_Programming/

Sequences

Lecture 01

COMPSCI 10523

Strings Strings are a sequence of characters

Strings also have a number of other functions that can be used split() is especially useful

>>> name = 'Andrew'>>> name[0]

Lecture 01

name

Andrew'A'

True

6>>> len(name)

>>> 'd' in name

>>> name + ' ' + 'Luxton-Reilly'

'Andrew Luxton-Reilly'

COMPSCI 10524

Exercise 3 Write a function that determines whether a given

string of text contains a vowel or not. The function should return True if the text contains a vowel.

Lecture 01

COMPSCI 10525

Lists Lists are a built-in type in Python

Use square brackets to signify a list Lists can contain any type of data, or any mixture of

datamy_list1 = [1, 2, 3]

my_list2 = ['Hello', 'Is', 'there', 'anybody', 'out', 'there?']

my_list3 = [1, 5.899, 'Hello']

my_list4 = [4, 2, 6, 9, 3]

my_list 4 2 6 9 3

Lecture 01

COMPSCI 10526

List functions Numerous list functions are supported

Use help(list) to find out the functions Examples:

>>> x = [1, 2, 3]>>> len(x)

Lecture 01

3

[1, 2, 3, 4]

[1, 2, 3, 5]>>> x += [5]

>>> x + [4]

>>> 3 in xTrue

1>>> x[0]

x 1 2 3

x 1 2 3 5

COMPSCI 10527

Lists of lists Since a list can contain anything, it can of course

contain a list

In memory

my_list = [[1, 2, 3], [4, 5, 6], [7], [8, 9]]

my_list0 1 2 3

1 2 30 1 2

4 5 60 1 2

70

8 90 1

Lecture 01

COMPSCI 10528

Exercise 4 Draw a diagram showing how the following list is

structured in memory:

my_list = [[1, 2], [[3, 4], [5, 6, 7]]]

Lecture 01

COMPSCI 10529

Slices of sequences A piece of a sequence can be obtained using the

following syntax sequence_name[x:y] where x is the index of the first element and y is the

index after the last element

>>> name = 'Andrew'>>> name[0:0]

Lecture 01

''

'A'

'ndr'

>>> name[0:1]

>>> name[1:4]

COMPSCI 10530

Slice step valueActually, the syntax allows for a third value, used to define the step size between elements included in the slice. If a value if omitted, it defaults to [start:end:1]

If the step size is negative, it starts at the end and steps backward towards the start.

>>> name = 'Andrew'>>> name[:4:2]

>>> name = 'Andrew'>>> name[::-1]

name A n d r e w

Positive Index

0 1 2 3 4 5

Negative index

-6 -5 -4 -3 -2 -1

Lecture 01

'ad'

'werdnA'

COMPSCI 10531

For loops Used to iterate through a sequence

numbers = [2, 3, 5, 7, 11]for i in numbers: print(i)

name = "Andrew"for c in name: print(c)

Lecture 01

235711

Andrew

Example01.py

COMPSCI 10532

While loops Used to execute code when the end condition is

unknownname = "Andrew Luxton-Reilly"i = 0while name[i] != ' ': i += 1print('Space is at position:', i)

Space is at position: 6

Lecture 01

Example01.py

COMPSCI 10533

Range Range is a special object in Python

Used to generate integer numbers within a range of values

Can iterate through the rangefor x in range(0, 5): print(x)

Lecture 01

01234

Example01.py

COMPSCI 10534

List comprehensions A list can be created using instructions that

appear within the square brackets

The general format is as follows:

Examples: To convert a string to a list of characters:

To generate all the even numbers between 1 and 20

my_list = [x for x in range(0, 10)]

[expression for variable in sequence]

my_list = [c for c in 'Andrew']

my_list = [n * 2 for n in range(1, 10)]

Lecture 01

COMPSCI 10535

Exercise 5 Write a list comprehension that generates all the

odd numbers between 1 and 50

Lecture 01

COMPSCI 10536

We can extend the syntax for a list comprehension to include a condition:

The general format is as follows:

Examples: Generate a list of the non-vowel letters that appear in

a string:

List comprehensions that use conditions

my_list = [x for x in range(0, 10) if x % 2 == 0]

[expression for variable in sequence if condition]

Lecture 01

>>> name = 'Andrew Luxton-Reilly'>>> vowels = 'aeiou‘>>> my_list = [c for c in name if c not in vowels]

['A', 'n', 'd', 'r', 'w', ' ', 'L', 'x', 't', 'n', '-', 'R', 'l', 'l', 'y']

COMPSCI 10537

Information in a list is stored contiguously in memory location of the information can be calculated location = start of the list + index * size of each

element

Efficiency issues It takes the same time to access any of the elements Slow to move elements around (i.e. add and delete

elements from within the list)

Features of lists

Lecture 01