2-1unsortedlists

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Unsorted Lists

Data Structures Section 2-1


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What is a list?

A list is a homogeneous collection ofelements.

Linear relationship between elements:

(1) Each element except the first one hasa unique predecessor.

(2) Each element except the last one has

a unique successor. Length: the number of items in the list.


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What is an unsorted list?

A list in which data items are placed inno particular order.

What is a sorted list?

A list in which data items are placed in aparticular order.

Key: a member of the class whose value isused to determine the order ofthe items inthe list.


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Operations

MakeEmpty Boolean IsFull

int LengthIs

RetrieveItem (ItemType& item, Boolean& found)

InsertItem (ItemType item)

DeleteItem (ItemType item)

ResetList

void GetNextItem (ItemType& item)


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RetrieveItem (ItemType& item,

Boolean& found)

Function: Retrieves list element whose keymatches item's key (if present).

Preconditions: (1) List has been initialized,

(2) Key member of item has been initialized.

Postconditions: (1) If there is an elementsomeItem whose keymatches item's key, thenfound=true and item is a copy ofsomeItem;otherwise, found=false and item is unchanged,(2) List is unchanged.


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InsertItem (ItemType item)

Function: Adds item to list

Preconditions:

(1) List has been initialized,

(2) List is not full,

(3) item is not in list.

Postconditions: item is in list.


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DeleteItem (ItemType item)

Function: Deletes the element whose keymatches item's key

Preconditions: (1) List has beeninitialized, (2) Key member of item hasbeen initialized, (3) There is only oneelement in list which has a key matching

item's key.

Postconditions: No element in list has a

key matching item's key.


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ResetList

Function: Initializes current position for

an iteration through the list.

Preconditions: List has been initialized

Postconditions: Current position is priorto first element in list.


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void GetNextItem (ItemType&

item) Function: Gets the next element in list.

Preconditions: (1) List has been

initialized,(2) Current position is defined

Postconditions: (1) Current position isupdated to next position, (2) item is acopy of element at current position.


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Unsorted List Implementation

template

class UnsortedType {public:

void MakeEmpty();

bool IsFull() const;

int LengthIs() const;

void RetrieveItem(ItemType&, bool&);void InsertItem(ItemType);

void DeleteItem(ItemType);

void ResetList();

bool IsLastItem()

void GetNextItem(ItemType&);

private:

int length;

ItemType info[MAX_ITEMS];

int currentPos;};


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Unsorted List Implementationtemplate

void UnsortedType::MakeEmpty(){

length = 0;}

templatebool UnsortedType::IsFull() const{

return (length == MAX_ITEMS);}

template

int UnsortedType::LengthIs() const{

return length;}

(cont.)


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template

void UnsortedType::RetrieveItem (ItemType& item,bool& found)

{

int location = 0;found = false;

while( (location < length) && !found)

if (item == info[location]) { found = true;

item = info[location]; }

elselocation++;

}

(cont.)


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template

void UnsortedType::InsertItem (ItemTypeitem){

info[length] = item;

length++;}

(cont.)


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(cont.)template

void UnsortedType::DeleteItem(ItemType item){

int location = 0;while(item != info[location])

location++;

info[location] = info[length - 1];length--;

}


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(cont.)template

void UnsortedType::ResetList(){

currentPos = -1;}

templatebool UnsortedType::IsLastItem(){

return(currentPos == length - 1);}

templatevoid UnsortedType::GetNextItem (ItemType& item){

currentPos++;item = info[currentPos];

}


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Write a client function that splits anunsAorted list into two unsorted lists

using the following specification.

SplitLists (UnsortedType list, ItemType item,UnsortedType& list1, UnsortedType&

list 2)

Function: Divides list into two lists according to the keyof item.

Preconditions: list has been initialized and is notempty.

Postconditions: list1 contains all the items of listwhose keys are less than or equal to items key. list2contains all the items of list whose keys are greaterthan items key.


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ItemType listItem;

list.ResetList();while ( !list.IsLastItem()) {

list.GetNextItem(listItem);

if(listItem > item) {

if (!list2.IsFull())

list2.InsertItem(listItem);

}

else {

if ( !list1.IsFull())

list1.InsertItem(listItem);

}

}

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