Linked Structures - Review Chapter 13

Linked Structures - Review Chapter 13

Instructor: Scott Kristjanson

CMPT 125/125

SFU Burnaby, Fall 2013

Wk14.1 Slide 2Slides based on Java Foundations 3rd Edition, Lewis/DePasquale/Chase

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Scott Kristjanson – CMPT 125/126 – SFU

Scope

Introduction to Linked Structures: Object references as links Linked vs. array-based structures Managing linked lists Linked implementation of a stack


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Linked Structures

An alternative to array-based implementations are linked structures

A linked structure uses object references to create links between objects

Recall that an object reference variable holds the address of an object


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Linked Lists

A Person object could contain a reference to another Person

public class Person{ private String name; private String addr; private Person next; // Link to Another Person object}

A series of Person objects could make up a linked list:


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Linked Non-Linear Structures

Links could also be used to form more complicated, non-linear structures

This is called a graph


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Linked Lists

There are no index values built into linked lists

To access each node in the list you must follow the references from one node to the next

Person current = firstPerson;

while (current != null)

{

System.out.println(current);

current = current.next;

}


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Linked Lists – Inserting a node in the Middle

1. Set the “next” member in obj to refer to the next object in the list2. Set the “next” member of the previous object to refer to the new object

1

2

x

obj

nextprev


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Linked Lists – Inserting a node at the front

Care must be taken to maintain the integrity of the links

To insert a node at the front of the list, first point the new node to the front node, then reassign the front reference


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Linked Lists – Deleting the First Node

To delete the first node, reassign the front reference accordingly

If the deleted node is needed elsewhere, a reference to it must be established before reassigning the front pointer


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Put Linked List Details into separate Node Class

So far we've assumed that the list contains nodes that are self-referential (Person points to a Person)

But often we'll want to make lists of objects that don't contain such references

Solution: have a separate Node class that forms the list and holds a reference to the objects being stored

Node

Person

Node Node Node Node Node

Person Person Person Person Person


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Doubly Linked Lists

There are many variations on the basic linked list concept

For example, we could create a doubly-linked list with next and previous references in each node and a separate pointer to the rear of the list

next

previous

Node

Person

Node

Person

Node

Person

Node

Person

Node

Person

Node

Person


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Implementing a Stack using Links

Let's implement a stack using a linked list to hold the elements

Our LinkedStack<T> class stores a generic type T and implements the same StackADT<T> interface used previously

A separate LinearNode<T> class forms the list and hold a reference to the element stored

An integer count will store how many elements are currently in the stack


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LinkedStack<T>

public class LinkedStack<T> implements StackADT<T>{ private int count; private LinearNode<T> top;

/** * Creates an empty stack. */ public LinkedStack() { count = 0; top = null; } LinearNode<T> top

int count

LinkedStack<T>

Linear

Node<T>


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LinearNode<T>

public class LinearNode<T>{ private LinearNode<T> next; private T element; public LinearNode() { next = null; element = null; }

public LinearNode(T elem) { next = null; element = elem; }

public LinearNode<T> getNext() { return next;} public void setNext(LinearNode<T> node) { next = node;} public T getElement() { return element;}

public void setElement(T elem) { element = elem;}}

LinearNode<t> next

T element

LinearNode<t> top

Object of Class T

Linear

Node<T>


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Since all activity on a stack happens on one end, a single reference to the front of the list will represent the top of the stack

LinearNode

T

LinearNode

T

LinearNode

T

LinearNode

T

LinearNode

T

LinearNode

T


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The stack after A, B, C, and D are pushed, in that order:


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After E is pushed onto the stack:


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package jsjf;

/**

* Represents a node in a linked list.

*

* @author Java Foundations

* @version 4.0

*/

public class LinearNode<T>

{

private LinearNode<T> next;

private T element;

/**

* Creates an empty node.

*/

public LinearNode()

{

next = null;

element = null;

}

/**

* Creates a node storing the specified element.

* @param elem element to be stored

*/

public LinearNode(T elem)

{

next = null;

element = elem;

}



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/** * Returns the node that follows this one. * @return reference to next node */ public LinearNode<T> getNext() { return next; } /** * Sets the node that follows this one. * @param node node to follow this one */ public void setNext(LinearNode<T> node) { next = node; } /** * Returns the element stored in this node. * @return element stored at the node */ public T getElement() { return element; } /** * Sets the element stored in this node. * @param elem element to be stored at this node */ public void setElement(T elem) { element = elem; }}



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package jsjf;

import jsjf.exceptions.*;import java.util.Iterator;

/** * Represents a linked implementation of a stack. * * @author Java Foundations * @version 4.0 */public class LinkedStack<T> implements StackADT<T>{ private int count; private LinearNode<T> top;

/** * Creates an empty stack. */ public LinkedStack() { count = 0; top = null; }



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/** * Adds the specified element to the top of this stack. * @param element element to be pushed on stack */ public void push(T element) { LinearNode<T> temp = new LinearNode<T>(element);

temp.setNext(top); top = temp; count++; }

/** * Removes the element at the top of this stack and returns a * reference to it. * @return element from top of stack * @throws EmptyCollectionException if the stack is empty */ public T pop() throws EmptyCollectionException { if (isEmpty()) throw new EmptyCollectionException("stack");

T result = top.getElement(); top = top.getNext(); count--; return result; }



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Key Things to take away:

Linked Objects:

• Object Reference variables can be used to create linked structures• A Linked List is composed on objects that each point to the next in the list• Objects stored in a collection should not contain any implementation

details of the underlying data structure that • The order in which references are changed are very important• Dealing with the first node in the list often requires special handling• A Linked List implementation of a Stack adds elements to, or removes

elements from, one end of the linked list.• Queues, Trees, and other structures can be created with Linked Objects


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Practice Array Questions

Problem 1: Write a program that shuffles a deck of cards, then deals out 5 cards each to two players.

Problem 2: Create a method that accepts two 2-dimensional arrays A and B as formal parameters and returns the matrix product A*B.

Problem 3: What is wrong with Bob’s Array code?

Problem 4: Write a method called sumArray that accepts an array of floating point values and returns the sum of the values stored in the array

Problem 5: Write a method called sum2DArray that accepts an int[][] array and sums all the numbers in the array and returns the sum of the values stored in the array.


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Problem 1: Write a program to shuffle and deal cards

Step 1: Create the Shuffled Deck using a Stack

for(int i=0; i<Card.numSuits*Card.numValues; i++) { boolean foundNextCard = false; int tries = 0;

while (!foundNextCard) { int cardValue = valueGen.nextInt(Card.numValues); int cardSuit = suitGen .nextInt(Card.numSuits ); tries++; if (cardDealt[cardSuit][cardValue] == false) { Card nextCard = new Card(cardValue+1, cardSuit); deckOfCards.push(nextCard); cardDealt[cardSuit][cardValue] = true; foundNextCard = true; System.out.println("Card "+(i+1)+" : "+ nextCard+" found after "+tries+" tries"); } }}


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Step 2: Deal five cards to each player

for(int p=0; p<numPlayers; p++)

for(int c=0; c<numCardsPerHand; c++)

hand[p][c] = deckOfCards.pop();


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Step 3: Display both player’s hands

for(int p=0; p<numPlayers; p++) {

System.out.println("\nPlayer "+p+" hand:");

for(int c=0; c<numCardsPerHand; c++) {

System.out.println(

"Card " + c + ": "+hand[p][c]);

}

}


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Discussion: How does a Card get converted to a String?System.out.println("Card "+c+": "+hand[p][c]);

Using the toString method from the Card class!

public String toString() { if (value == 0) return "Joker"; else return cardNames[value]+" of "+suit; }

enum Suit {Hearts, Diamonds, Clubs, Spades};

private final static String[] cardNames = {"Joker","Ace", "Two", "Three","Four","Five", "Six", "Seven","Eight","Nine","Ten", "Jack","Queen","King"};


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Problem 2: Method to return the matrix product A*B.

public static int[][] matrixMultiply(int[][] A, int [][] B) {int aRows = A.length;int aCols = A[0].length;int bRows = B.length;int bCols = B[0].length;

int N = A.length; // Assume A and B are both NxN

if (aCols != bRows) throw new IllegalArgumentException( "A Columns: " + aCols + " did not match number of B Rows " + bRows); int[][] C = new int[aRows][bCols]; for (int i = 0; i < aRows; i++) // A Row for (int j = 0; j < bCols; j++) // B Column for (int k = 0; k < aCols; k++) // A Column C[i][j] += A[i][k] * B[k][j];

return C;}


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And the Winner for best TicTacToe GUI is…

Curtis Babnik

Human vs Smarter: http://www.youtube.com/watch?v=nZyvR0v3ixsHuman vs Learns : http://www.youtube.com/watch?v=t87UFMKbegE


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TicTacToe UML

A UML Diagram using a Eclipse UML Plugin:


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References:

1. J. Lewis, P. DePasquale, and J. Chase., Java Foundations: Introduction to Program Design & Data Structures. Addison-Wesley, Boston, Massachusetts, 3rd edition, 2014, ISBN 978-0-13-337046-1

Linked Structures - Review Chapter 13

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