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    Kotlin
    Java

    • Linked Lists : 45

    • Algorithms and Lists : 44

    • Lambda Expressions : 43

    • Anonymous Classes : 42

    • Practice with Interfaces : 41

    • Implementing Interfaces : 40

    • Using Interfaces : 39

    • Working with Exceptions : 38

    • Throwing Exceptions : 37

    • Catching Exceptions : 36

    • References and Polymorphism : 35

    • References : 34

    • Data Modeling 2 : 33

    • Equality and Object Copying : 32

    • Polymorphism : 31

    • Inheritance : 30

    • Data Modeling 1 : 29

    • Companion Objects : 28

    • Encapsulation : 27

    • Constructors : 26

    • Objects, Continued : 25

    • Introduction to Objects : 24

    • Compilation and Immutability : 23

    • Practice with Collections : 22

    • Maps and Sets : 21

    • Lists and Type Parameters : 20

    • Imports and Libraries : 19

    • Multidimensional Arrays : 18

    • Practice with Strings : 17

    • null : 16

    • Algorithms and Strings : 15

    • Strings : 14

    • Functions and Algorithms : 13

    • Practice with Functions : 12

    • More About Functions : 11

    • Errors and Debugging : 10

    • Functions : 9

    • Practice with Loops and Algorithms : 8

    • Algorithms I : 7

    • Loops : 6

    • Arrays : 5

    • Compound Conditionals : 4

    • Conditional Expressions and Statements : 3

    • Operations on Variables : 2

    • Variables and Types : 1

    • Hello, world! : 0

    Algorithms and Lists

    interface SimpleList {
    fun get(index: Int): Any?
    fun set(index: Int, value: Any?)
    fun remove(index: Int): Any?
    fun add(index: Int, value: Any?)
    }
    class SimpleArrayList(private var values: Array<Any?>) : SimpleList {
    override fun get(index: Int): Any? {
    require(index in values.indices)
    return values[index]
    }
    override fun set(index: Int, value: Any?) {
    require(index in values.indices)
    values[index] = value
    }
    override fun remove(index: Int): Any? {
    TODO("Not implemented!")
    }
    override fun add(index: Int, value: Any?) {
    TODO("Not implemented!")
    }
    override fun toString() = values.contentToString()
    }
    val list = SimpleArrayList(arrayOf("you", "are", "not", "alone"))

    Welcome back! The rest of the course is incredibly exciting material. We’ll begin building and analyzing new data structures and algorithms, while also introducing new bits of Java syntax along the way.

    Algorithms and Data Structures
    Algorithms and Data Structures

    Algorithms and data structures comprise the core conceptual concerns of computer science. Algorithms are how we do things. Data structures are how we represent things.

    The two topics are intertwined. We will implement data structures to support certain algorithms. And we will design algorithms that utilize specific data structure capabilties.

    Algorithm Analysis
    Algorithm Analysis

    As we proceed, we will spend more time talking about how long certain algorithms take and why—or performing algorithm analysis. To do this we use something called Big-O notation to describe the behavior of algorithms. Let’s define those terms:

    Algorithm analysis: the determination of the computational complexity of algorithms, that is the amount of time, storage and/or other resources necessary to execute them.

    Big-O notation is a mathematical notation that describes the limiting behavior of a function when the argument tends towards a particular value or infinity.

    Complexity Categories
    Complexity Categories

    We’ll take a very high-level view of Big-O as we get started with algorithm analysis. Let’s provide an overview of the different complexity categories that we’ll learn to identify, and some of the code features that are associated with them.

    Array Lists
    Array Lists

    To get some practice with algorithm analysis, over the next few lessons we’ll be implementing a data structure known as a list. You’ve already been working with Kotlin’s built-in Lists, so this will give you a peek at how they are actually implemented.

    Lists store a sequence of elements. We already know how to do that using arrays, and we can build an implementation of lists on top of an array. Let’s see how!

    // Initial SimpleArrayList

    Remove
    Remove

    OK, this is good start. But so far all we have is a wrapper around an array! That’s not particularly interesting.

    Indeed, the key difference between an array and list is that the size of the list can change. But doing this using a list that maintains are array internally requires more work. Let’s see how, starting with the remove operation. (You get to implement add as this lesson’s homework.)

    // SimpleArrayList remove

    Practice: SimpleArrayList get and set

    Created By: Geoffrey Challen
    / Version: 2020.10.0

    Let's begin building a simple list implementation that uses arrays to store the values. Create a class SimpleArrayList with a public constructor that initializes the list using a passed non-nullable array of Any? references. Your array should be private.

    Next, implement:

    1. fun get(Int): Any, which takes an Int index and returns the Any at that index
    2. fun set(Int, Any?), which takes an Int index and an Any reference and sets that value at the index to the passed reference.

    Both your get and set method should require that the index passed is valid for that SimpleArrayList. Here's an example of how your SimpleArrayList should work:

    Don't overthink this! Both get and set should be two lines of code (including one for the require).

    List Method Algorithm Analysis
    List Method Algorithm Analysis

    Next, let’s take a look at our core list functions and see how they perform. We’re going to use our new big-O vocabulary and try to understand the performance of get, set, and remove.

    // SimpleArrayList performance

    Homework: SimpleArrayList add

    Created By: Geoffrey Challen
    / Version: 2020.10.0

    Let's write the add method for our SimpleArrayList. First, create a SimpleArrayList class with a single public constructor that initializes the list with a passed non-null array of Any? references. Call the array values and provide a public getter but not a public setter. (This setter is purely for testing.) Also provide a method size() with that returns the current size of the list.

    Now write the add method, which takes the position to add at as an Int as its first parameter and the Any? reference to add as its second. add should add the element to the list, increasing the size by one and shifting elements after the add position backward. You should assert that the passed position is valid for this list. But note that you should allow adding a new item to the end of the existing list.

    When you are done, here is how your SimpleArrayList class should work:

    CS People: Mark Dean
    CS People: Mark Dean

    Mark Dean was a pioneering Black American computer scientist, engineer, and inventor, who made important contributions to several computing technologies. He developed the ISA bus, an early computer standard allowing interconnection of hardware components. He also worked on computer graphics and the first chip to achieve a 1 GHz clock rate(1).

    In recognition of his many accomplishments, Mark Dean was the first African-American to be named an IBM Fellow. Watch the following short video to learn more about Mark Dean:

    More Practice

    Need more practice? Head over to the practice page.