E.G.M. Petrakis lists, stacks, queues 1

Lists

• List: finite sequence of data elements– Ordered: each element has a position in list– All elements has the same data type– The operations depend on the type of the list

and not on the data type• List: the most general type

• Stacks, Queues: restricted versions of lists– Not all operations are allowed

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listinfo

next

list

New element

Insertions

current

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list

list

Deleted element

Deletions

current

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• Terminology:– Empty: contains no elements– Length: number of elements in list– Head, or list: pointer to the beginning of the list– Tail: pointer to the last element– Current: pointer to current element– Ordered: elements in ascending/descending

order

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• Operations on lists:– setFirst: set “current” to “Head” – setPos(i): sets current to the i-th element – currValue: returns value of “current” element– next/prev: “current” points to next/prev element– clear: delete all elements– insert: inserts an element in current position– append: inserts an element at “tail”– remove: delete the “current” element – find(k): set current to the first occurrence of “k”– isInList: true/false if current position is in list– isEmpty: true/false if list is empty

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class list { // List class ADT in C++public:

list(const int = LIST_SIZE); //constructor~list( ); //destructorvoid clear ( ); // remove all elementsvoid insert(const ELEM &); // inset at currentvoid append(const ELEM&); // insert at tailELEM remove ( ); // remove currentvoid setFirst ( ); // set current to HEADvoid prev ( ) ; // set current to previousvoid next ( ); // set current to nextint length ( ) const; // return size of listvoid setPos(const int); // set current to new posvoid setValue(const ELEM&) // set current’s valuesbool isEmpty( ) const; // true/false on emptybool isInList( ) const; // true/false if current is in listbool find(const ELEM&); // find value of current in list

};

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• Iterate through the whole list: MyList

for (MyList.first( ); MyList.isInList(); MyList.next( ) DoSomething(MyList.currValue( ));

• If MyList: (12 32 15) and current points to 32 then MyList.insert(90) changes the list to be (12 32 90 15)

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• Implementation, two approaches:– Array-based

• The elements are stored in array

• Fixed size

• Fast implementation

• Actual number or element less than size allocated

– Linked list• Dynamic: allocates memory for new elements

• No restriction on number of elements except physical memory size

• Slower but more efficient

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• Array implementation (1) : – Stores elements in continuous array positions– Head of list at pos 0– Insertion/deletion causes shifting of elements

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class list{ //Array based list classprivate:

int msize //Maximum size of listint numinlist //Actual number of ELEMsint curr; //Position of “current”ELEM* listarray; //Array holding ELEMs

 Public:

list (const int=LIST_SIZE); // Constructor~list(); // Destructorvoid clear(); // Remove all ELEMs from listvoid insert(const ELEM&); // Insert ELEM at current positionvoid append(const ELEM&); // Insert ELEM at tail of listELEM remove(); // Remove and return current ELEMvoid setFirst(); // Set curr to first position;void prev(); // Move curr to previous position;void next(); // Move curr to next position;int length() const; // Return current length of listvoid setPos(const int); // Set curr to specified positionvoid setValue(const ELEM&); // Set current ELEM's valueELEM currValue() const; // Return current ELEM's valuebool isEmpty() const; // Return TRUE if list is emptybool isInList() const; // TRUE if curr is within listbool find(const ELEM&); // Find value (from current position)

};

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List::List(int sz) // Constructor: initialize { msize = sz; numinlist = 0; curr = 0; listarray = new Elem[sz]; }

List::~List() // Destructor: return array space { delete [] listarray; }

void List::clear() // Remove all Elems from list { numinlist = 0; curr = 0; } // Simply reinitialize values

void List::insert(const Elem item) { // Insert Elem at current position // Array must not be full and curr must be a legal position assert((numinlist < msize) && (curr >=0) && (curr <= numinlist)); for(int i = numinlist; i > curr; i--) // Shift Elems up to make room listarray[i] = listarray[i - 1]; listarray[curr] = item; numinlist++; // Increment current list size }

void List::append(const Elem item) { // Insert Elem at tail of list assert(numinlist < msize); // List must not be full listarray[numinlist++] = item; // Increment list size }

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Elem List::remove( ) { // Remove and return current Elem assert( !isEmpty() && isInList() ); // Must be an Elem to remove Elem temp = listarray[curr]; // Store removed Elem for (int i=curr; i < numlist-1; i++) // shift elements down listarray[i] = listarray[i+1]; numinlist--; // Decrement current list size return temp;}

void List::setFirst( ) // Set curr to first position { curr = 0; }

void List::prev( ) // Move curr to previous position { curr--; }

void List::next( ) // Move curr to next position { curr++; }

int List::length( ) const // Return current length of list { return numinlist; }

void List::setPos(int pos) // Set curr to specified position {curr = pos; }

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void List::setValue(const Elem val) { // Set current Elem's value assert(isInList( )); // Curr must be at valid position listarray[curr] = val; }

Elem List::currValue( ) const { // Return current Elem's value assert(isInList( )); // Must be at a valid position return listarray[curr]; }

bool List::isEmpty( ) const // Return TRUE if list is empty { return numinlist == 0; }

bool List::isInList( ) const // TRUE if curr is within list { return (curr >= 0) && (curr < numinlist); }

bool List::find(int val) { // Find value (starting at curr) while (isInList( )) // Stop if reach end if (key(currValue( )) == val) return TRUE; // Found it else next( ); return FALSE; // Not found

}

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• Array implementation(2): pointers to elems

1 115 26list

1 11

11 12

5 10

26 0

8

9

10

11

12

13

nodes

NULL

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313 14 376 5 12List 1

17 26List 2

31 19 32List 3

1 18 13 11 4 15List 4

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1 26 0

2 11 10

3 5 16

4 1 25

5 17 1

6 13 2

7

8 19 19

9 14 13

10 4 22

11

12 31 8

13 6 3

14

15

16 37 24

17 3 12

18

19 32 0

20

21 7 9

22 15 0

23

24 12 0

25 18 6

List 4List 2

List 3

List 1

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class list { //Array based list classprivate:

int msize //Maximum size of listint numinlist //Actual number of ELEMsint curr; //Position of “current”

int next; // next element int avail; // next available position

ELEM* listarray; //Array holding ELEMs plus pointers to next ELEMsint get_node( ); //get position of available nodevoid free_node( ); //return node in arrayvoid insert(p, x); //insert node after the node pointed by pvoid delete(p, x); //delete node after the node pointed by p

public:list (const int=LIST_SIZE); // Constructor~list( ); // Destructorvoid clear( ); // Remove all ELEMs from listvoid insert(const ELEM&); // Insert ELEM at current positionvoid append(const ELEM&); // Insert ELEM at tail of listELEM remove( ); // Remove and return current ELEMvoid setFirst( ); // Set curr to first position;void prev( ); // Move curr to previous position;void next( ); // Move curr to next position;int length( ) const; // Return current length of list………. // More member functions

};

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list::list(int sz) { // Constructor: initialize msize = sz; numinlist = 0; curr = 0; listarray = new Elem[sz]; // put all (available) elements in a stack avail = 0; // the first available element for (i=0; i < msize; i++) listarray[i].next = i+1; // each elements points to its

successor listarray[msize-1].next = nothing; // the last elem has no next }

list::~list( ) // Destructor: return array space { delete [] listarray; }

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int list::get_node( ) { if (avail == nothing) error(‘list overflow’) else { int pos = avail; avail = listarray[avail].next; return pos; }}

void list::free_node (int p) { node[p].next = avail; avail =p;}

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void insert::list (int p, int x) { if (p == null) error (‘void insertion’) else { int q = get_node( ); node[q].info = x; node[q].next = node[p].next; node[p].next=q; }}void delete::list (int p; int x) { if ( p == 0) error (‘void deletion’); else { int q = node[p].next; x = node[q].info; node[p].next = node[q].next; free_node(q); }}

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• Linked List implementation: makes use of pointers to elements– Allocates memory for new elements as needed– Each node is a distinct object

• The node class Class link { // A linked-list node public:

ELEM element // node valuelink *next; // pointer to next nodelink(const ELEM& val, link *nextval = NULL);{element = val; next = nextval;}link(link *nextval = NULL) {next = nextval;} ~link( ) { }

}

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class List { // Linked list class private: Link* head; // Pointer to list header Link* tail; // Pointer to last Elem in list Link* curr; // Position of "current" Elem public: List( ); // Constructor ~List( ); // Destructor void clear( ); // Remove all Elems from list void insert(const Elem); // Insert Elem at current position void append(const Elem); // Insert Elem at tail of list Elem remove( ); // Remove and return current Elem void setFirst( ); // Set curr to first position void prev( ); // Move curr to previous position void next( ); // Move curr to next position int length( ) const; // Return current length of list void setPos(int); // Set curr to specified position void setValue(const Elem); // Set current Elem's value Elem currValue( ) const; // Return current Elem's value bool isEmpty( ) const; // Return TRUE if list is empty bool isInList( ) const; // TRUE if curr is within list bool find(int); // Find value (from current position) };

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List::List( ) // Constructor { head = new Link; tail = head; curr = head; } // Initialize

List::~List( ) { // Destructor while(head != NULL) { // Return link nodes to free store curr = head; head = headnext; delete curr; } }

void List::clear( ) { // Remove all Elems from list while (headnext != NULL) { // Return link nodes to free

store curr = headnext; // keeps header node !! headnext = currnext; // otherwise, similar to ~List( ) delete curr; } curr = head; tail = head; // Reinitialize }

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void List::insert(const Elem item) // Insert Elem at current position { assert(curr != NULL); // Must be pointing to list Elem currnext = new Link(item, currnext); if (tail == curr) // Appended new Elem tail = currnext; }

void List::append(const Elem item) // Insert Elem at tail of list { tail = tailnext = new Link(item, NULL); }

Elem List::remove( ) { // Remove and return current Elem assert(isInList( )); // Must be valid position in

list Elem temp = currnextelement; // Remember value Link* ltemp = currnext; // Remember link node currnext = ltempnext; // Remove from list if (tail == ltemp) tail = curr; // Removed last Elem: set tail delete ltemp; // Send link to free store return temp; // Return value removed }

void List::setFirst( ) // Set curr to first position { curr = head; }

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void List::next( ) // Move curr to next position { if (curr != NULL) curr = currnext; }

void List::prev( ) { // Move curr to previous position

Link* temp = head; if ((curr == NULL) || (curr == head)) // No previous Elem { curr = NULL; return; } // so just return while ((temp!=NULL) && (tempnext != curr)) temp=tempnext; curr = temp; }

int List::length( ) const { // Return current length of list int cnt = 0; for (Link* temp = headnext; temp != NULL; temp = tempnext) cnt++; // Count Elems and return cnt; }

void List::setPos(int pos) { // Set curr to specified position curr = head; for (int i = 0; (curr != NULL) && (i < pos) i++) curr = currnext;}

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void List::setValue(const Elem val) { // Set current Elem's value assert(isInList()); currnext->element = val; }

Elem List::currValue() const // Return value of current Elem { assert(isInList( )); return currnextelement; }

bool List::isEmpty() const // Return TRUE if list is empty { return headnext == NULL; }

bool List::isInList() const // TRUE if curr is within list { return (curr != NULL) && (currnext != NULL); }

bool List::find(int val) { // Find value (starting at curr) while (isInList( )) if (key(currnext->element) == val) return TRUE; else curr = currnext; return FALSE; // Not found

}

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• Comparison of implementations– Array-Based Lists:

• Insertion and deletion are (n) instead of (1) • Prev and direct access are (1) instead of (n) • Array must be allocated in advance• No overhead if all array positions are full• Faster in some cases

– Linked Lists:• Insertion and deletion are (1) • Prev and direct access are (n)• Space grows with number of elements• Every element requires overhead

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• Doubly linked list: allows direct access to both next and previous elements of the current pointer– insert (delete) operations update both next/prev

pointers– Easy implementation

curr next = new (item, currnext, curr);

if (currnext != NULL)

currnextprev = currnext

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current

current

Insertion in doubly linked list

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current

current

Deletion from doubly linked list

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• Circular linked lists: the next pointer of the last element points to the first element– The tail points is no longer needed– Implementation: left as an exercise