technomess

Tuesday, 6 June 2017

Class Relationships

Please read these two resources to have a better understanding of class relationships

http://creately.com/blog/diagrams/class-diagram-relationships/ focus on association, composition/aggregation (depends on your IA), multiplicity and inheritance. http://www.infoworld.com/article/3029325/application-development/exploring-association-aggregation-and-composition-in-oop.html (link title explains itself)

For more resources on the principles of OOP and UML diagrams, click here.

These are my favourite explanations (so far) regarding the principles of OOP: Abstraction, Encapsulation, Inheritance and Polymorphism. They are most important to understand and remember, so study and practice them well. The links have page names (at the end of the link) that are self-explanatory.

UML provides so many tools, that it can be overwhelming. So it is always useful to narrow it down and focus on what is useful for a specific task. The following resources are on UML class diagrams. You are also recommended to look into use-case diagrams, which are great for conceptual designs.

In terms of class relationships, you should know (according to the IBO syllabus content)

dependency (“uses”)
aggregation (“has a”) and
inheritance (“is a”).

You may find the following links useful to revise these concepts. Just focus on what IBO requires among all the detailed information provided.

Tuesday, 25 April 2017

FDE Cycle

Fetch-Decode-Execute Cycle

Links with information about the FDE cycle, from simple & concise to deeper and more detailed:

GCSE Bytesize (Instructions)
The Fetch–Execute cycle and the role of registers within it (A level Computing WikiBook)
Also known as the Instruction cycle (Wikipedia article)

An excellent flow chart depicting the FDE cycle (original source https://en.wikipedia.org/wiki/Instruction_cycle):

Plus a nice animation demonstrating how the fetch-decode-execute cycle works, made using Scratch:

https://scratch.mit.edu/projects/2145440/

I have also made my own, simplified version for study and revision purposes:

Monday, 24 April 2017

Sorting and Searching Algorithms

Resources, animations and videos of sorting and searching algorithms:

The following links point to videos and video channels showing animations of different sorting algorithms. More than one video is provided so that you may pick the one you understand best. You could also build your understanding from a few sources as well.

https://visualgo.net/ - excellent interactive animated sorting algorithms out there
http://www.sorting-algorithms.com - sorting algorithm animations, discussed
https://www.geeksforgeeks.org/fundamentals-of-algorithms/ self-explanatory
http://xoax.net/comp_sci/crs/algorithms/ - concise and well illustrated videos about different algorithms.
http://www.cs.armstrong.edu/liang/animation/ - animations on algorithms, plus data structures and other topics.
https://www.youtube.com/user/AlgoRythmics/videos - algorithms illustrated with European traditional folk dances

Sequential (Linear) and Binary searches:

https://www.geeksforgeeks.org/linear-search/
https://www.geeksforgeeks.org/binary-search/
https://youtu.be/wNVCJj642n4 (Both)
https://youtu.be/vZWfKBdSgXI (Linear search only)
https://youtu.be/CX2CYIJLwfg (Linear search only)
https://youtu.be/5xlIPT1FRcA (Binary search only)
https://youtu.be/D5SrAga1pno (Binary search only)

Bubble sort:

https://youtu.be/P00xJgWzz2c

Selection sort:

https://youtu.be/Aq2E47uU2ao

https://youtu.be/6nDMgr0-Yyo

Insertion sort:

https://www.geeksforgeeks.org/comparison-among-bubble-sort-selection-sort-and-insertion-sort/

Sunday, 23 April 2017

Algorithms and Abstract Data Types HL

Resources about various algorithms - Higher Level:

http://www.algolist.net/Algorithms/ - various algorithms (sort, binary search) and programming concepts (recursion) explained
From this link, be sure to revise the sequential and binary searches, plus the chapters on sorting algorithms and recursion (code examples are on Python, which means it's close to pseudocode, but you can run it if you have the Python 3 interpreter)
http://introcs.cs.princeton.edu/java/40algorithms/ - an excellent chapter on Algorithms and Data Structures; there was a performance question in a recent past paper, so it may be a good idea to read 4.1 (performance) as well. Don't obsess over Tilde notation and skip memory usage as well. Our focus is to be aware of how some algorithms are more efficient than others (as you can see by their classification into their order of growth: constant, logarithmic, linear, quadratic, cubic, exponential, etc.)

Stacks and Queues

Binary Search Trees

Resources about Abstract Data Types:

http://www.webopedia.com/TERM/A/abstract-data-type.html
http://www.csanimated.com/animation.php?t=Abstract_data_type
http://www.csanimated.com/animation.php?t=Stack
http://www.csanimated.com/animation.php?t=Queue
http://www.csanimated.com/animation.php?t=Linked_list
http://visualgo.net/en/list.html - animated ADTs (linked list implementations)
Chapter on Linked Lists, from the same site as #2 in the previous list of links ;-)
http://www.algolist.net/Data_structures/ - well explained and clear diagrams
HackerRank's algorithms YoutTube playlist
HackerRank's data structures YoutTube playlist
mycodeschool's YouTube playlist on data structures. Examples are in C/C++, but their explanations and diagrams are great!

2D Arrays and IB Pseudocode

This brief post shows how to create a bi-dimentional array and describe it using IB pseudocode. It isn't stated in the IB Pseudocode in Examinations or Approved notation for developing pseudocode documents, so it's my answer to it, not an official one. Don't sue me if your examiner disagrees with me! O_o

declare A as integer array of size [ROWS][COLUMNS] or
declare A as integer array of size (ROWS, COLUMNS)
declare A as integer array of size [5][6]
declare A as integer array of size (5, 6)

Obviously, integer should be replaced by the appropriate data type.
IB papers may have defined it for you, or they may not ask you at all to define the size. You could define it (unknown size) as

declare A as integer array of size [ ][ ]

...then you'd use it like

loop ROW from 0 to 5
    loop COL from 0 to 6
        output A[ROW][COL]     or    output A(ROW, COL) 
    end loop
end loop

I'd recommend going for the [ ][ ] style as it'd be more consistent with the single dimensional arrays described in the IB pseudocode documents mentioned above.

Arrays and Java

Just a short post with pretty much all you need to know about arrays in Java:

http://javabeginnerstutorial.com/core-java-tutorial/java-array-tutorial/ to start with
http://www.homeandlearn.co.uk/java/java_arrays.html excellent site, from start to end; includes 2D arrays and much more

http://introcs.cs.princeton.edu/java/14array/ great resource with many examples, but more complex
Also, it is highly recommended to study Big Java Late Objects (Horstmann, 2013) - chapter 6: Arrays and Array Lists

Below are some additional links about arrays and 2D arrays: