15-121 Introduction to Data Structures 1 September 2020 Margaret - - PowerPoint PPT Presentation

15-121 Introduction to Data Structures

1 September 2020 Margaret Reid-Miller

Fall 2020 15-121 (Reid-Miller) 2

Today

• Course Logistics
• Course Topics
• A (very basic) Java introduction
• Course website:

https://www.cs.cmu.edu/~mrmiller/15-121

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Me

Margaret Reid-Miller mrmiller@cs.cmu.edu Gates 6003, x 8-2640 I am an

• Assistant Teaching Professor
• CS Upperclass Academic Advisor

What to call me? Margaret, please (or formally, Professor Reid-Miller)

You

• Take 15-121 if you are an IS major, or if you don’t

plan to take CS core courses.

• Take 15-122 if you are a CS or ECE major or minor,
• r plan to take more CS classes.
• Why learn Java?
• One of the most common languages used in

industry.

• Used for large applications
• It's objected-oriented.

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Fall 2020 15-121 (Reid-Miller) 6

Office Hours

For extra help on the class material or assignments you may reach

• ut to our two Teaching Assistants or me.

Office Hours: (tentatively) Sean Tavares (TA): Saturday 2:00 pm – 4:00 pm Leah Watko (TA): Sunday 2:00 pm – 4:00 pm Margaret: Monday 10:00 am – 12:00pm (noon) Other times by appointment Assignments are due Monday nights. What office-hour times are best for you?

OHQueue

• During office hours, when you have a question open

your personal Zoom meeting.

• Go to the OHQueue (see webpage sidebar) and

select 15-121 P (not 15-121 Q). It may be the last in the list.

• (You can pin 15-121 P to the top of the list by clicking

the red asterisk.)

• Include a link to your Zoom meeting in the Question

part.

• When it is your turn a TA or I will join your Zoom

meeting to help you.

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Prerequisites

• Formally: 15-112
• You will need:
• Laptop or desktop computer
• The Java JDK and an editor or IDE

– Eclipse (what I will use in class) – DrJava (only runs Java 6 on Mac) Under Resource, see Extra Help for instructions on how to install Java JDK and Eclipse

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Why Data Structures?

Data structures are ways to organize and store data and perform operations on the data efficiently.

• Understand and create new algorithms
• Analyze algorithms (time/space efficiency)
• Which data structures we use will depend on
• What operations we expect to perform often on our

data.

• What are performance tradeoffs for access/update.
• Efficient algorithms are essential with big data.

(Think Google, databases, Amazon, Facebook,…)

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Introduction to Data Structures

• This course provides a foundation for organizing

large data sets for efficiency. Two parts:

• Conceptual information about various data structures
• How to use and implement those data structures in

your programs.

• We assume you know how to write programs using

fundamental programming concepts (variables, booleans, conditional, loops, functions, lists, …)

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Course elements

• Lectures: Notes and code will be posted to

website

• Participation – 5%
• Recitation labs – 5%
• Quizzes – 10%
• Homework – 40%
• 2 Midterms – 20%: 10% each
• Final – 20%

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Lectures over Zoom

• Recordings will be put on Canvas
• Be prepared to take notes, and have paper and

pen/pencil. I often ask you to write code or draw figures, and may ask you to turn in what you write.

• Answer and ask lots of questions (It helps your

classmates who are equally curious and it gives me feedback.)

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Participation 5%

• You must attend lectures, ask questions, and

submit in-class exercises.

• If you miss a couple of days of class, you may

still earn 100% for participation.

• If you miss class half the time, you will earn

0% for participation.

• If attending lectures synchronously is difficult,

please email me to make alternative arrangements.

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Wednesday Recitations 5%

• In person and remote
• There will be (~12) weekly labs of short coding
• exercises. Only 10 count towards your grade.
• You must attend and participate to get credit.
• You are encouraged to work collaboratively.
• Submitting after class will not be accepted.
• I will post solutions after class.

Tomorrow’s recitation, though, will be a lecture!

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Homework 40%

• There will be weekly assignments that include a

written portion and programming.

• Due Monday nights at 11:59 pm.
• You are allowed up to 4 late days total without

penalty, with a maximum of 2 late days per assignment.

• No credit will be given for late work after you have

used up all your late days.

• I recommend you submit often (even if incomplete)
• ne day before and again one hour before its due.

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Quizzes 10%

• Most weeks on Thursday there will be short

quiz (15-20 minutes).

• It will test the previous week’s work.
• We will drop your lowest TWO quizzes.
• There will be no make-up quizzes for any

reason.

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2 Written Midterms 10% each

• Midterm Exams will be in class on
• Thursday, Oct 8
• Tuesday, Nov 9

(Dates may change, see schedule)

• No makeup exams except by prior approval

by me for

• medical or family emergencies
• pre-arranged university-approved

absences

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Final Exam 25%

• During final exams.
• We will not proctor the final exam prior to the

registrar scheduled exam (makeup day is Dec 21).

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Disabilities

• If you suspect or have a documented

disability, you may be eligible to receive accommodations from the Office of Disability Resources (access@andrew.cmu.edu)

• Please use their online system to notify me

and to discuss your needs early in the semester.

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Fall 2020 15-121 (Reid-Miller) 20

Today

ü Course Logistics ➤Overview of Course

• A (very basic) Java introduction

Course Topics

• Java Objects, Arrays, ArrayLists, Efficiency
• Big-O, Linked Lists, Recursion,
• Interfaces, Iterators, Stacks & Queues
• Searching & Sorting, Trees, BSTs, Recursion
• Sets & Maps, Hashing, Priority Queues,
• Heaps, (Graphs), Review & Final Exam

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Fall 2020 15-121 (Reid-Miller) 22

Today

ü Course Administration ü Overview of Course ➤A (very basic) Java introduction

Executing Code

• Java and Python are high-level programming languages

(human readable) created in a text editor.

• Programs in high-level languages (source code)

cannot be run by the computer directly.

• Program translation converts source code to a low-level

target language.

• This target or machine code uses only a small set of

instructions specific to the machine.

• Run-time is the period when the computer is executing

commands.

• The operating system copies the machine code from

disk to memory and starts running it directly.

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Program Translation

• Compiler is a program that translates code in a high-

level source language, all at once, into low-level target language.

• E.g., Java is compiled to bytecode.
• The source code is translated only once.
• The target code can be executed many times.
• Interpreter - program that translates each statement

and then executes it, one at a time, much like a human interpreter

• E.g., Python is interpreted, also to bytecode

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Traditional Compilation

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Windows Intel Linux HP Linux IBM Mac OS X iMac Source code Machine code Machine code Machine code Machine code compile Source code Source code Source code Different hardware/operating systems need slight variants of each program and separate compilers.

Java Translation

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JVM - Java Virtual Machine

JVM Linux HP Windows Intel Linux IBM Mac OS X iMac

Game.java Game.class (bytecode)

Compile (or compile) Interpret JVM JVM JVM Java compiles to a single “virtual” machine.

Types of Programming Errors

• Compile-time errors - Syntax errors found by the

compiler or syntax-aware editors (e.g., Eclipse).

• e.g., x - * y =
• Run-time errors - Error causes program to stop

abnormally; often called an exception.

• e.g., x = y / z (What if z is zero?)
• Logical errors - Program produces incorrect results

without complaint.

• e.g., Sort program that runs to completion but

does not always sort the data

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Java vs Python Syntax

• In Python, indentation is semantic (has meaning)
• E.g., indentation delimits statement blocks
• In Java, indentation is recommended
• We require it in this class, however, for style

and readability.

• Instead, in Java statement blocks are surrounded

by curly braces {} and most statements end in semi-colons.

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Java program structure

• Every Java program consists of one or more

classes:

• Each class contains methods:

– Each method contains the statements to execute

• Everything is Java must have a type.
• Every Java program starts its execution at a

method called main.

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public class <name> { <method> <method> … <method> }

All Java code are inside classes

• The basic form of a Java class is at follows:

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Keywords are in purple Same name as the file name

Every Java program must have a method named main

• The program execution starts at the main method.

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public static void main (String[] args) { <statement> <statement> … <statement> } method header grouping characters return type argument type

A simple program

/* * Prints three lines to the console. */ public class DreamDisplayer { public static void main(String[] args) { System.out.println("When I grow up ... "); System.out.println(); // blank line System.out.print("I want to be "); System.out.println(”an astronaut."); } }

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Comments println: adds newline at end. print: stays on same line System.out: where to find the method. Statements end with semicolons

OUTPUT: When I grow up ... I want to be an astronaut.

Our first program

• Your first homework is to do 20 problems on
• CodingBat. It is due next Tuesday at

11:55pm (a day later than usual)

• Let’s use CodingBat to write our first Java

program.

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