1 chapter 16 linked structures dale/weems/headington

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Chapter 16

Linked Structures

Dale/Weems/Headington

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Chapter 16 Topics

Meaning of a Linked List Meaning of a Dynamic Linked List Traversal, Insertion and Deletion of Elements

in a Dynamic Linked List Specification of a Dynamic Linked Sorted List Insertion and Deletion of Elements in a

Dynamic Linked Sorted List

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What is a List?

A list is a varying-length, linear collection of homogeneous elements.

linear means each list element (except the first) has a unique predecessor, and each element (except the last) has a unique successor

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To implement the List ADT

The programmer must

1) choose a concrete data representation for the list, and

2) implement the list operations

Array-Based Sorted List Operations

Transformers Insert Delete

Observers IsEmpty IsFull Length IsPresent Print

change state

observe state

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Array-based class SortedList

IsFull

Length

IsPresent

Delete

IsEmpty

Insert

Print

Private data:

length

data [ 0 ] [ 1 ] [ 2 ]

[MAX_LENGTH-1]

SortedList

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// SPECIFICATION FILE ARRAY-BASED SORTED LIST ( slist.h )const int MAX_LENGTH = 50 ;typedef int ItemType ;

class SortedList{public : // public member functions

SortedList ( ) ; // constructorbool IsEmpty ( ) const ;bool IsFull ( ) const ; int Length ( ) const ; // returns length of list void Insert ( ItemType item ) ; void Delete ( ItemType item ) ; bool IsPresent( ItemType item ) const ;void Print ( ) ;

private : // private data members

int length ; // number of values currently storedItemType data[MAX_LENGTH] ; void BinSearch ( ItemType item, bool& found, int& position ) const ;

} ; 7

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How to Implement a List

use a built-in array stored in contiguous memory locations, implementing operations Insert and Delete by moving list items around in the array, as needed

use a linked list (to avoid excessive data movement from insertions and deletions) not necessarily stored in contiguous memory locations

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Implementation Possibilities for a List ADT

List

Linked listBuilt-in array

Built-in dynamic data and pointers

Built-in arrayof structs

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A Linked List

a linked list is a list in which the order of the components is determined by an explicit link member in each node

the nodes are structs--each node contains a component member and also a link member that gives the location of the next node in the list

head ‘X’ ‘C’ ‘L’

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Dynamic Linked List

head “Ted” “Irv” “Lee”

in a dynamic linked list, nodes are linked together by pointers, and an external pointer (or head pointer) points to the first node in the list

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Nodes can be located anywhere in memory

the link member holds the memory address of the next node in the list

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// Type DECLARATIONS

struct NodeType {

char info;

NodeType* link;

}

typedef NodeType* NodePtr;

// Variable DECLARATIONS

NodePtr head;

NodePtr ptr;

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Declarations for a Dynamic Linked List

. info . link

‘A’ 6000

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Pointer Dereferencing and Member Selection

. info . link

‘A’ 6000 ptr

ptr

ptr

. info . link

‘A’ 6000

*ptr

ptr

. info . link

(*ptr).info

ptr->info

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ptr is a pointer to a node

. info . link

‘A’ 6000 ptr

ptr

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*ptr is the entire node pointed to by ptr

ptr

. info . link

‘A’ 6000

*ptr

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ptr->info is a node member

ptr

. info . link

ptr->info

(*ptr).info // equivalent

‘A’ 6000

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ptr->link is a node member

ptr

. info . link

ptr->link

(*ptr).link // equivalent

‘A’ 6000

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Traversing a Dynamic Linked List

//PRE: head points to a dynamic linked list

ptr = head ;

while (ptr != NULL) {

cout << ptr->info ;

// Or, do something else with node *ptr

ptr = ptr->link ;

}

ptr

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ptr = head ;


cout << ptr->info ;


ptr = ptr->link ;

}

ptr 3000

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ptr = head ;


cout << ptr->info ;


ptr = ptr->link ;

}

ptr 3000

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head


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ptr = head ;


cout << ptr->info ;


ptr = ptr->link ;

}

ptr 3000

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ptr = head ;


cout << ptr->info ;


ptr = ptr->link ;

}

ptr 5000

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ptr = head ;


cout << ptr->info ;


ptr = ptr->link ;

}

ptr 5000

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ptr = head ;


cout << ptr->info ;


ptr = ptr->link ;

}

ptr 5000

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ptr = head ;


cout << ptr->info ;


ptr = ptr->link ;

}

ptr 2000

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ptr = head ;


cout << ptr->info ;


ptr = ptr->link ;

}

ptr 2000

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ptr = head ;


cout << ptr->info ;


ptr = ptr->link ;

}

ptr 2000

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head


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ptr = head ;


cout << ptr->info ;


ptr = ptr->link ;

}

ptr NULL

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ptr = head ;


cout << ptr->info ;


ptr = ptr->link ;

}

ptr NULL

3000 “Ted” 5000 “Irv” 2000 “Lee” NULL

3000 5000 2000

head


Using Operator new

If memory is available in an area called the free store (or heap), operator new allocates the requested object, and returns a pointer to the memory allocated.

The dynamically allocated object exists until the delete operator destroys it.

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Inserting a Node at the Front of a List

char item = ‘B’;

NodePtr location;

location = new NodeType;

location->info = item;

location->link = head;

head = location;


‘B’item

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NodePtr location;




head = location;


‘B’item

location

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NodePtr location;




head = location;


‘B’item

location

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NodePtr location;




head = location;


‘B’item

location ‘B’

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NodePtr location;




head = location;


‘B’item

location ‘B’

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NodePtr location;




head = location;


‘B’item

location ‘B’

The object currently pointed to by the pointer is deallocated, and the pointer is considered undefined. The object’s memory is returned to the free store.

Using Operator delete

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Deleting the First Node from the List

NodePtr tempPtr;

item = head->info;

tempPtr = head;

head = head->link;

delete tempPtr;

head

item

‘B’ ‘X’ ‘C’ ‘L’

tempPtr

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NodeType * tempPtr;

item = head->info;

tempPtr = head;

head = head->link;

delete tempPtr;

head

item

‘B’ ‘X’ ‘C’ ‘L’

tempPtr

‘B’

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NodeType * tempPtr;

item = head->info;

tempPtr = head;

head = head->link;

delete tempPtr;

head

item

‘B’ ‘X’ ‘C’ ‘L’

tempPtr

‘B’

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NodeType * tempPtr;

item = head->info;

tempPtr = head;

head = head->link;

delete tempPtr;

head

item

‘B’ ‘X’ ‘C’ ‘L’

tempPtr

‘B’

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NodeType * tempPtr;

item = head->info;

tempPtr = head;

head = head->link;

delete tempPtr;

head

item

‘X’ ‘C’ ‘L’

tempPtr

‘B’

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What is a List?

a list is a varying-length, linear collection of homogeneous elements

linear means each list element (except the first) has a unique predecessor, and each element (except the last) has a unique successor

ADT SortedList2 Operations

Transformers InsertTop Insert DeleteTop Delete

Observers Print IsEmpty

change state

observe state

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// SPECIFICATION FILE DYNAMIC-LINKED SORTED LIST( slist2.h )

typedef int ItemType ; // Type of each component // is simple type or string type

struct NodeType{

ItemType item ; // Pointer to person’s nameNodeType* link ; // link to next node in list

} ;

typedef NodeType* NodePtr;

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struct NodeType

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// SPECIFICATION FILE DYNAMIC-LINKED SORTED LIST( slist2.h )

class SortedList2{public :

bool IsEmpty ( ) const ;

void Print ( ) const ;

void InsertTop ( /* in */ ItemType item ) ;

void Insert ( /* in */ ItemType item ) ;

void DeleteTop ( /* out */ ItemType& item ) ;

void Delete ( /* in */ ItemType item );

SortedList2 ( ) ; // Constructor~SortedList2 ( ) ; // DestructorSortedList2 ( const SortedList2& otherList ) ; // Copy-constructor

private :

NodeType* head;} ;

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class SortedList2

Print

~SortedList2

Insert

InsertTop

SortedList2

IsEmpty

Delete

‘C’ ‘L’ ‘X’

Private data:

head

DeleteTop

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Insert Algorithm

what will be the algorithm to Insert an item into its proper place in a sorted linked list?

that is, for a linked list whose elements are maintained in ascending order?

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Insert algorithm for SortedList2

find proper position for the new element in the sorted list using two pointers prevPtr and currPtr, where prevPtr trails behind currPtr

obtain a node for insertion and place item in it

insert the node by adjusting pointers

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Implementing SortedList2Member Function Insert

// DYNAMIC LINKED LIST IMPLEMENTATION (slist2.cpp)

void SortedList2 :: Insert ( /* in */ ItemType item )

// PRE: item is assigned && List components in ascending order

// POST: item is in List && List components in ascending order{

.

.

.

}

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Inserting ‘S’ into a Sorted List

‘C’ ‘L’ ‘X’

Private data:

head

prevPtr currPtr

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Finding Proper Position for ‘S’

‘C’ ‘L’ ‘X’

Private data:

head

prevPtr currPtr

NULL

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‘C’ ‘L’ ‘X’

Private data:

head

prevPtr currPtr


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‘C’ ‘L’ ‘X’

Private data:

head

prevPtr currPtr


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‘C’ ‘L’ ‘X’

Private data:

head

prevPtr currPtr

Inserting ‘S’ into Proper Position

‘S’

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// IMPLEMENTATION DYNAMIC-LINKED SORTED LIST (slist2.cpp)

SortedList2 ::SortedList2 ( ) // Constructor

// Post: head == NULL

{

head = NULL ;

}

SortedList2 :: ~SortedList2 ( ) // Destructor

// Post: All linked nodes deallocated

{

ItemType temp ;

// keep deleting top node

while ( !IsEmpty )

DeleteTop ( temp );

}57

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void SortedList2 :: Insert( /* in */ ItemType item ) // Pre: item is assigned && list components in ascending order

// Post: new node containing item is in its proper place

// && list components in ascending order

{ NodePtr currPtr ;

NodePtr prevPtr ;

NodePtr location ;

location = new NodeType ;

newNodePtr->link = item ;

prevPtr = NULL ;

currPtr = head ;

while ( currPtr != NULL && item > currPtr->info )

{ prevPtr = currPtr ; // advance both pointers currPtr = currPtr->link ;

}

location->link = currPtr ; // insert new node here

if ( prevPtr == NULL )

head = location ;

else

prevPtr->link = location ;

}58

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void SortedList2 :: DeleteTop ( /* out */ ItemType& item )

// Pre: list is not empty && list elements in ascending order

// Post: item == element of first list node @ entry

// && node containing item is no longer in linked list

// && list elements in ascending order

{

NodePtr tempPtr = head ;

// obtain item and advance head

item = head->info ;

head = head->link ;

delete tempPtr ;

}

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void SortedList2 :: Delete ( /* in */ ItemType item ) // Pre: list is not empty && list elements in ascending order

// && item == component member of some list node

// Post: item == element of first list node @ entry

// && node containing first occurrence of item is no longer

// in linked list && list elements in ascending order

{ NodePtr delPtr ;

NodePtr currPtr ; // Is item in first node?

if ( item == head->info )

{ delPtr = head ; // If so, delete first node

head = head->link ;}

else { // search for item in rest of list

currPtr = head ;

while ( currPtr->link->info != item )

currPtr = currPtr->link ;

delPtr = currPtr->link ;

currPtr->link = currPtr->link->link ;}

delete delPtr ;

}60

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class SortedList2

Print

~SortedList2

Insert

InsertTop

SortedList2

IsEmpty

Delete

‘C’ ‘L’ ‘X’

Private data:

head

DeleteTop

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