Chapter 4 Unordered List 1 Learning Objectives Describe

Chapter 4 Unordered List 1

Learning Objectives ● ● Describe the properties of an unordered list. Study sequential search and analyze its worstcase and average running times. Discover how the entries of a list may be dynamically rearranged at achieve better search times. Understand the public interface of an unordered list class in Java and the running times of its methods. 2

Learning Objectives ● ● ● Develop a set of classes for an expense processing application based on an unordered list. Understand how object-oriented programming can be used to write a single piece of code in Java that can perform equality checking based on different criteria for different input objects. Learn what linked lists are, why they are useful, and how to build and manipulate them. 3

Learning Objectives ● ● Implement a linked lest class in Java and analyze the running times of its methods. Implement an unordered list class in Java using a linked list component. 4

4. 1 Unordered List Properties ● Keeping track of daily expenses. It would be useful to write a program that maintains an expense list of all recorded expenses, that can be used to find quick answers to simple budgeting type questions. 5

4. 1 Unordered List Properties 6

4. 1 Unordered List Properties 7

4. 1 Unordered List Properties ● Answer the following questions: What is the maximum (or minimum) expense, and on what item? What is the average expense? What is the total amount spent on a given item? ● All these question may be answered by scanning such a list from the beginning and terminating when our question is answered. 8

4. 1 Unordered List Properties 9

4. 2 Sequential Search ● Operation contains searches for a specific itme in the list. Since the list is unordered, the only way to conduct the search is to look at every element in the sequence. If a match is found, the operation returns true, otherwise it returns false. 10

4. 2 Sequential Search 11

4. 2 Sequential Search ● Best case ● Worst case ● 1 n Unsuccessful search? n 12

Unordered. List implementation using array List: array of element 13

Insert method ● insert(“Rami”) 14

Delete method 1 - define loc =0 2 - search for item in array list using loop. If item in the list 3 - assign item index to loc. 4 - store last element of array “list” in index = loc 5 - num. Items -Else Print element not in the list 15

Delete method 16

delete(“Judy”) 17

Unordered. List class

4. 3 A List Class ● No. Such. Element. Exception thrown back. 19

4. 3 A List Class 20

4. 3 A List Class 21

4. 3 A List Class ● Example that enumerates: 22

4. 3 A List Class ● Running times An implementation should be able to access the last item of the list in O(1) time, so that the add method may be implemented in O(1) time. Maintain a count of the number of items in the list. ● The size method can then simply return this count. Use a cursor to enumerate a list, so that each of the enumeration methods first and next may be implemented in O(1) time. 23

4. 4 An Expense. List Class Using List ● An Expense. List class would support operations for maintaining expenses. Use the generic List class as a component, implementing all the Expense. List class methods by reusing code from one or more of the appropriate List class methods. Every expense will consists of the amount of expense and the item on which the expense was incurred. 24

4. 4. 1 Expense Class Interface 25

4. 4. 1 Expense Class Interface 26

4. 4. 2 Expense Class 27

4. 4. 2 Expense Class 28

4. 4. 3 Expense. List Class Interface 29

4. 4. 3 Expense. List Class Interface 30

4. 4. 4 Expense. List Class Implementation Wrong 31

4. 4. 4 Expense. List Class Implementation ● min. Expense, and ave. Expense scan every expense entry in the list. 32

4. 4. 5 Equality of Objects and Searching ● Rewrite the method by implementing a search in the method. 33

4. 4. 5 Equality of Objects and Searching ● The notion of equality is defined by the equals method of the exp object. Two expenses are equal if they have the same amount and item. What if we wanted the equality based only on the item so if two expenses have the same item with different amount they are equal. We would need to redefine the equality of expenses in terms of item only. 34

4. 4. 5 Equality of Objects and Searching ● About Keys The get method is useful to extract an entire object from the list by matching its key part with a specified key. 35

4. 4. 5 Equality of Objects and Searching ● Only use the key part, (ex item )and get returns the entire matching entry (including amount), if any. What data structure should be used to store the items in a list? ● Removing items from anywhere in the list. ● Leaves holes in the array. Uses more space than necessary. Search times would be greater than O(n). If the holes are patched up by compacting the array, we would be doing a lot of data movement within the array. 36

4. 5 Linked List 37

4. 5 Linked List ● To access the entries of the linked list, a reference to its first entry is all we need. One can access any entry by simply following the chain of links. When an entry is removed from some place in a linked list, all that needs to be done is to have its predecessor's link refer to its successor. Similarly, an entry may be inserted anywhere in the list without having to move other entries over to create space. 38

4. 5 Linked List 39

4. 5 Linked List ● The biggest drawback of the linked list is its inability to perform random accesses for any entry in a single step. 40

4. 5. 1 Node 41

4. 5. 1 Node ● A node is defined in terms of itself: next field of the node class is a reference to another Node<T> object. Self-referential structure 42

4. 5. 2 Insertion ● Adding to the beginning of the list. 43

4. 5. 2 Insertion ● Adding in between two nodes. 44

4. 5. 2 Insertion ● Adding to the end of the list 45

4. 5. 3 Deletion ● Deleting the last node, or in-between node. ● Deleting the first node ● L = L. next 46

4. 5. 3 Deletion ● In both insertion and deletion we assumed the existence of P, a reference to the node just prior to the one to be inserted or deleted. 47

4. 5. 4 Access ● Stepping through, or traversing, all the entries of a linked list from beginning to end following the chain of references is a useful operation in practice. 48

4. 5. 4 Access ● Deleting the first occurrence of the string “Carrot”. 49

4. 5. 4 Access ● We can't delete next. Node unless we have a reference to the node prior to it. 50

Unordered. List implementation using Linked List ● Insert list = null empty list Insert(“john”) 51

Insert ● insert(“Becca”) 52

Delete ● delete(“Lila”) 53

● delete(“Kate”) 54

delete(“John”) 55

delete last node in the list ● delete(“Becca”) ● list = null 56

4. 5. 5 Circular Linked List ● It is useful to have instant access to both the first and the last entries of a linked list. 57

4. 5. 5 Circular Linked List ● Given that L refers to the last entry, the first entry is simply L. next. if L==L. next, that means there is exactly one entry in the CLL. 58

4. 5. 5 Circular Linked List ● Insertion Inserting a new node as the first entry? Will not work if the list is empty. 59

4. 5. 5 Circular Linked List ● Deletion Deleting the last node. Wee need to have access to the node preceding it. Assume that P is this predecessor node, and that it has already been located. Assumes there at least two nodes in the list. The termination condition is that the scanning pointer returns to the starting position. 60