MIS215 Module 0 - Intro 1 MIS 215 Module 0 Intro to Data Structures.
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Transcript of MIS215 Module 0 - Intro 1 MIS 215 Module 0 Intro to Data Structures.
MIS215 Module 0 - Intro 1
MIS 215 Module 0Intro to Data Structures
MIS215 Module 0 - Intro 2
Where are we?
Intro toJava, Course
Java lang.basics
Arrays
Introduction
Newbie Programmers Developers ProfessionalsDesigners
MIS215
Binary Search
SearchTechniques Sorting Techniques
Bubblesort
Basic Algorithms
Fast Sorting algos(quicksort, mergesort)
Hashtables
Graphs,Trees
LinkedLists
Stacks,Queues
List Structures Advanced structures
MIS215 Module 0 - Intro 3
Today’s Buzzwords Data Structures Algorithms Efficiency of algorithms Analysis of algorithms Programming = Data Structures + Algorithms Programming as a problem-solving method
Elluminate
Nuts and Bolts of this Class Elluminate
A tool for Synchronous Online Collaboration This course will be all about collaboration Start by clicking the link in the Course Calendar in
WebCT Allow Elluminate to install Do not click on the microphone while in class! (believe
me – bad things will happen if you do)
Dr. Java and JDK 1.5
MIS215 Module 0 - Intro 4
Elluminate features we will use Definitely:
Private and moderator chatsDrawing boardPolling and quizzing
Possibly:Project presentationsOut-of-class meetingsOnline office hours
MIS215 Module 0 - Intro 5
MIS215 Module 0 - Intro 6
Introduction to Data Structures What are data structures/ruptures & algorithms
good for? Overview of data structures. Overview of algorithms Some definitions OO programming S/W engineering Java Library Data Structures
MIS215 Module 0 - Intro 7
What’s a program? So, far, if you’ve only done CS
208/209/equivalent, what has a program been?
Probably, just doing some simple data manipulation..store some grades in an arrayaverage the grades, find min/maxanything else??
MIS215 Module 0 - Intro 8
Overview of Data Structures
Arrays (unordered and ordered) Stacks, Queues, Lists
why did I lump these all together? Trees (binary, red-black [?], 2-3-4 [?]) Hash table Heap
MIS215 Module 0 - Intro 9
Our approach to Problem Solving this quarter
Dr. Java Integrated Development Environment Edit – Compile – Test – Debug Unfortunately CaTS won’t install in labs Fortunately it doesn’t take much to install Lets use Dr. Java to write our first program
MIS215 Module 0 - Intro 10
HelloWorld.java
public class HelloWorld {
public void run() { System.out.println("Hello Java World!"); }
public static void main (String [] args) { HelloWorld tpo = new HelloWorld(); tpo.run(); }}
MIS215 Module 0 - Intro 11
Dissecting HelloWorld
Every program in Java is (at least) one class Each class has one or more methods. The class that runs the program is the main
class, and has a main(…) method Typically, you should create an instance of a
class in your main method, and call methods of that instance
That’s exactly what HelloWorld Does!
MIS215 Module 0 - Intro 12
Lets do a little more…public class GradeCalculator {
private int score = 843; // Score of the student
public void run() {
char letgrade = ''; //single quotes for characters
// Do what is needed here to find the letter grade
System.out.println("The student's letter grade is" +
letgrade);
}
public static void main (String [] args) {
GradeCalculator gc = new GradeCalculator();
gc.run();
}
}
MIS215 Module 0 - Intro 13
Dissecting GradeCalculator
First finish it .. What is the logic for finding the letter
grade from the numeric score? What is that “private int score;” business? What are our alternatives?
MIS215 Module 0 - Intro 14
The Input Class A stable class for easily receiving input from the
users Documentation of this class is available at
http://www.wright.edu/~arijit.sengupta/mis215/samples/complexity/Input.html
How do you use it? Create an instance of the Input class Call the appropriate method (with or without an
argument) Why should you use the Input class?
Stable – includes some built-in error checks!
MIS215 Module 0 - Intro 15
Lets try it! Change GradeCalculator to ask the user
for the numeric score Where should you create the Input class? What happens if you call the run() method
multiple times? What is a better way?
MIS215 Module 0 - Intro 16
Going ahead – practising loops
Write a program that asks the user to guess a number between 1 and 100.
In a loop, let the computer make a guess, and the user says G/L/M (greater/less/match)
Continue until you get a match Report the number of tries
MIS215 Module 0 - Intro 17
CFC – Comment-First Coding What is it? Why comments?
Descriptive Think in English instead of the cryptic code Will always compile!!! Self-documenting
Why comment-first? How do you fill out the comments? Lets try it!
MIS215 Module 0 - Intro 18
Only the run() method now..public void run() { // Step 1. Initialization
// Step 2.
// Step 3.
// Step 4.
// Step 5.
}
MIS215 Module 0 - Intro 19
Lets describe the stepspublic void run() { // Step 1. Initialization // set up the needed variables
// Step 2.
// Step 3.
// Step 4.
// Step 5.
}
MIS215 Module 0 - Intro 20
Finally, fill in the codepublic void run() { // Step 1. Initialization // set up the needed variables int steps = 0, guess = 0; // any other variables? // Step 2.
// Step 3.
// Step 4.
// Step 5.
}
MIS215 Module 0 - Intro 21
Now what? Practice CFC – we will try to use this
diligently this quarter. Every assignment you submit must have
your names as comments at the top of the file, and all code must be extensively commented, preferably CFC-ed
Did I just make up a verb there?
MIS215 Module 0 - Intro 22
Finally…
Lets try to have fun as you write code Remember, programs do what we tell them to do
– so we are the boss! There is nothing like “IT is not working” – IT
always works – just like you tell it to – maybe you didn’t tell it to do the right thing!
Practice, practice, practice… makes it perfect
Part 2 – Analysis of Algorithms There are many different ways to solve the
same problem How do you tell if one way would be better
than another? Analysis of algorithms is a method for
identifying the efficiency of an algorithm
MIS215 Module 0 - Intro 23
Order Notation (big-Oh/little-oh) For this course, we are only going to use
the big Oh notation An algorithm is described to have the
complexity of O(some function over n) For example, Mergesort has the
complexity O(n lg n) No – that wasn’t a typo – lg(n) is log2(n)
MIS215 Module 0 - Intro 24
So what does it mean? Lets first see how these functions behave:
MIS215 Module 0 - Intro 25
n n2 lg(n) n lg(n) 2n n!
10 100 4 34 1024 3628800
100 10000 7 665 1.26765E+30 9.3326E+157
1000 1000000 10 9966 1.0715E+301 #NUM!
5000 25000000 13 61439 #NUM! #NUM!
10000 100000000 14 132878 #NUM! #NUM!
50000 2500000000 16 780483 #NUM! #NUM!
100000 10000000000 17 1660965 #NUM! #NUM!
So.. Can you compare now? Complexity of Bubblesort is O(n2), and
complexity of Mergesort is O(n lg n). Which one is more efficient?A. Bubblesort
B. Mergesort
C. Both are the same
MIS215 Module 0 - Intro 26
How do you determine complexity of an algorithm? Typically involves mathematical induction For the purpose of this class, try to find the
main loop of the algorithm, and determine the number of comparisons (or whichever is the most important operation is)
Try to find an association between the input and the number of operations
MIS215 Module 0 - Intro 27
The ComplexityDemo.java program Compile and run it – don’t worry too much
about the source code at the moment See how the time behaves as you run the
different algorithms If you feel adventurous, change the code a
bit and try different input numbers (careful – some will not run for large
inputs)MIS215 Module 0 - Intro 28