Linked Lists Comp 1402/1002 Using Defined Types Data Structures - - PDF document

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Linked Lists

Comp 1402/1002

Using Defined Types

Data Structures are key to Computer Science

• JAVA libraries:

– Vector, – ArrayList, – Hashtable…

• C

– Arrays

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Arrays

• Properties

– Elements are consecutive in memory – Easy to determine location in memory – Access a single element quickly – But CANNOT change size

• declare new space
• Copy all elements (at times)

– May not correspond to amount of data

Alternative

• Properties

– Easily grows to an arbitrary size – Correspond to amount of data – Less rigid

• Possible alternative are lists

– Singly linked list – Doubly linked list – Trees (binary trees, 2-3 trees, finger trees, B-trees…)

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Lists

• Lists can be viewed as chains

– Each piece of information is a link – Links are independent of each other – Links are somehow connected to each other

• Properties

– Elements are in arbitrary location – Must view all predecessors to find one – Grows to arbitrary size – Massive re-orderings possible quickly

Processing a List

Lists can be viewed as chains Begin at the beginning of the list (chain)

• first element is the first link
• second element is the second link
• third element is the third link

Could be arbitrary length

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Singly Linked Lists Single Link per Element

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What is in a NODE ?

Each element (NODE) in a list contains:

• Data
• a pointer to another NODE

How will we define the NODE type ?

Global Declarations !

typedef int KEY_TYPE; /*applic dependent*/ typedef struct { KEY_TYPE key; … /* other data */ } DATA; typedef struct nodeTag { DATA data; struct nodeTag *link; /* Link is ptr to node */ } NODE;

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List Orderings

Three main types of lists:

Time dependent

• 1. First in First out - FIFO (queue)
• 2. Last in First out - LIFO (stack)

Key dependent

• 3. Sorted list

Maintaining a List

• Access the list

– Keep a pointer to the first NODE (for now)

NODE * pList; /* pList is a pointr to first node */

• r

NODE *head; /* head is a pointer to first node */

• All functions modifying a list

– Must have access to the list (Take pList as a parameter) – e.g.:

NODE *insertNode(NODE *pList...);

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Insert a Node

• 1. Allocate memory
• 2. Locate predecessor (A pointer , pPre)
• 3. Point new node to its successor
• 4. Point predecessor to new node

Meanings of pPre

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Insert into Empty List Insert Node at Beginning

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Insert Node in Middle Insert Node at End

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Deleting a Node

Still requires the predecessor’s location!

• Remove the node
• Free the memory space !

Delete First Node

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Delete General Case Searching Through a List

Search should return:

• If a match exists

– A pointer to the node containing the key

• If there is no match

– NULL – A pointer to the largest element that is smaller or equal to the key (for a sorted list)

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Traverse Linked Lists

printList, averageList, …

searchList

int searchList (NODE *pList, NODE **pPre, NODE **pCur, KEY_TYPE target) { . . . }

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Inserting a Node

NODE * insertNode(NODE *pList, NODE *pPre, DATA data) { . . . }

Deleting a Node

NODE * deleteNode(NODE *pList, NODE *pPre) { . . . }