Linked Structures - Review Chapter 13

1. Linked Structures - Review Chapter 13 Instructor: Scott Kristjanson CMPT 125/125 SFU Burnaby, Fall 2013

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

3. 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

4. Linked Lists • A Personobject 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 Personobjects could make up a linked list:

5. Linked Non-Linear Structures Links could also be used to form more complicated, non-linear structures This is called a graph

6. 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; }

7. Linked Lists – Inserting a node in the Middle • Set the “next” member in obj to refer to the next object in the list • Set the “next” member of the previous object to refer to the new object obj 1 2 x prev next

8. 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 frontreference

9. 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 frontpointer

10. Put Linked List Details into separate Node Class Node Node Node Node Node Node Person Person Person Person Person Person So far we've assumed that the list contains nodes that are self-referential (Personpoints to a Person) But often we'll want to make lists of objects that don't contain such references Solution: have a separate Nodeclass that forms the list and holds a reference to the objects being stored

11. Doubly Linked Lists next Node Node Node Node Node Node previous Person Person Person Person Person Person There are many variations on the basic linked list concept For example, we could create a doubly-linked list with nextand previousreferences in each node and a separate pointer to the rear of the list

12. 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

13. Linear Node<T> 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; • } LinkedStack<T> LinearNode<T> top int count

14. 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> top Linear Node<T> LinearNode<t> next T element Object of Class T

15. Implementing a Stack using Links Linear Node Linear Node Linear Node Linear Node Linear Node Linear Node T T T T T T 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

16. Implementing a Stack using Links The stack after A, B, C, and D are pushed, in that order:

17. Implementing a Stack using Links After E is pushed onto the stack:

18. Implementing a Stack using Links 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; }

19. Implementing a Stack using Links /** * 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; } }

20. Implementing a Stack using Links 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; }

21. Implementing a Stack using Links /** * 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; }

22. Implementing a Stack using Links

23. 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

24. 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.

25. 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"); • } • } • }

26. Problem 1: Write a program to shuffle and deal cards • 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();

27. Problem 1: Write a program to shuffle and deal cards • 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]); • } • }

28. Problem 1: Write a program to shuffle and deal cards • 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"};

29. Problem 2: Method to return the matrix product A*B. • publicstaticint[][] 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; • }

30. And the Winner for best TicTacToe GUI is… • Curtis Babnik • Human vs Smarter: http://www.youtube.com/watch?v=nZyvR0v3ixs • Human vs Learns : http://www.youtube.com/watch?v=t87UFMKbegE

31. TicTacToe UML • A UML Diagram using a Eclipse UML Plugin:

32. References: • 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