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C++ Plus Data Structures

C++ Plus Data Structures. Nell Dale Chapter 5 Linked Structures Modified from the slides by Sylvia Sorkin, Community College of Baltimore County - Essex Campus. Definition of Stack.

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C++ Plus Data Structures

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  1. C++ Plus Data Structures Nell Dale Chapter 5 Linked Structures Modified from the slides by Sylvia Sorkin, Community College of Baltimore County - Essex Campus

  2. Definition of Stack • Logical (or ADT) level:A stack is an ordered group of homogeneous items (elements), in which the removal and addition of stack items can take place only at the top of the stack. • A stack is a LIFO “last in, first out” structure.

  3. Stack ADT Operations • MakeEmpty -- Sets stack to an empty state. • IsEmpty -- Determines whether the stack is currently empty. • IsFull -- Determines whether the stack is currently full. • Push (ItemType newItem) -- Adds newItem to the top of the stack. • Pop (ItemType& item) -- Removes the item at the top of the stack and returns it in item. 3

  4. ADT Stack Operations Transformers • MakeEmpty • Push • Pop Observers • IsEmpty • IsFull change state observe state 4

  5. Another Stack Implementation • One advantage of an ADT is that the kind of implementation used can be changed. • The dynamic array implementation of the stack has a weakness -- the maximum size of the stack is passed to the constructor as parameter. • Instead we can dynamically allocate the space for each stack element as it is pushed onto the stack.

  6. char letter = ‘V’; StackType< char > myStack; myStack.Push(letter); myStack.Push(‘C’); myStack.Push(‘S’); if ( !myStack.IsEmpty( ) ) myStack.Pop( letter ); myStack.Push(‘K’); Tracing Client Code ‘V’ letter

  7. Tracing Client Code ‘V’ letter Private data: topPtr NULL char letter = ‘V’; StackType< char > myStack; myStack.Push(letter); myStack.Push(‘C’); myStack.Push(‘S’); if ( !myStack.IsEmpty( ) ) myStack.Pop( letter ); myStack.Push(‘K’);

  8. Tracing Client Code letter ‘V’ Private data: topPtr ‘V’ char letter = ‘V’; StackType< char > myStack; myStack.Push(letter); myStack.Push(‘C’); myStack.Push(‘S’); if ( !myStack.IsEmpty( ) ) myStack.Pop( letter ); myStack.Push(‘K’);

  9. Tracing Client Code letter ‘V’ Private data: topPtr ‘C’ ‘V’ char letter = ‘V’; StackType< char > myStack; myStack.Push(letter); myStack.Push(‘C’); myStack.Push(‘S’); if ( !myStack.IsEmpty( ) ) myStack.Pop( letter ); myStack.Push(‘K’);

  10. Tracing Client Code letter ‘V’ Private data: topPtr ‘S’ ‘C’ ‘V’ char letter = ‘V’; StackType< char > myStack; myStack.Push(letter); myStack.Push(‘C’); myStack.Push(‘S’); if ( !myStack.IsEmpty( ) ) myStack.Pop( letter ); myStack.Push(‘K’);

  11. Tracing Client Code letter ‘V’ Private data: topPtr ‘S’ ‘C’ ‘V’ char letter = ‘V’; StackType< char > myStack; myStack.Push(letter); myStack.Push(‘C’); myStack.Push(‘S’); if ( !myStack.IsEmpty( ) ) myStack.Pop( letter ); myStack.Push(‘K’);

  12. Tracing Client Code letter ‘S’ Private data: topPtr ‘C’ ‘V’ char letter = ‘V’; StackType< char > myStack; myStack.Push(letter); myStack.Push(‘C’); myStack.Push(‘S’); if ( !myStack.IsEmpty( ) ) myStack.Pop( letter ); myStack.Push(‘K’);

  13. Tracing Client Code letter ‘S’ Private data: topPtr ‘K’ ‘C’ ‘V’ char letter = ‘V’; StackType< char > myStack; myStack.Push(letter); myStack.Push(‘C’); myStack.Push(‘S’); if ( !myStack.IsEmpty( ) ) myStack.Pop( letter ); myStack.Push(‘K’);

  14. ‘A’6000 .info .next Dynamically Linked Implementation of Stack // DYNAMICALLY LINKED IMPLEMENTATION OF STACK #include "bool.h" #include "ItemType.h" // for ItemType template<class ItemType> struct NodeType { ItemType info; NodeType<ItemType>* next; } 14

  15. // DYNAMICALLY LINKED IMPLEMENTATION OF STACK continued template<class ItemType> class StackType { public: StackType( ); // constructor // Default constructor. // POST: Stack is created and empty. void MakeEmpty( ); // PRE: None. // POST: Stack is empty. bool IsEmpty() const; // PRE: Stack has been initialized. // POST: Function value = (stack is empty) bool IsFull( ) const; // PRE: Stack has been initialized. // POST: Function value = (stack is full) 15

  16. // DYNAMICALLY LINKED IMPLEMENTATION OF STACK continued void Push( ItemType item ); // PRE: Stack has been initialized. // Stack is not full. // POST: newItem is at the top of the stack. void Pop( ItemType& item ); // PRE: Stack has been initialized. // Stack is not empty. // POST: Top element has been removed from stack. // item is a copy of removed element. ~StackType( ); // destructor // PRE: Stack has been initialized. // POST: Memory allocated for nodes has been // deallocated. private: NodeType<ItemType>* topPtr ; }; 16

  17. StackType MakeEmpty Private data: topPtr IsEmpty IsFull Push Pop ~StackType class StackType<char>

  18. Implementing a Stack as a Linked Structure

  19. // DYNAMICALLY LINKED IMPLEMENTATION OF STACK continued // member function definitions for class StackType template<class ItemType> StackType<ItemType>::StackType( ) // constructor { topPtr = NULL; } template<class ItemType> void StackType<ItemType>::IsEmpty( ) const // Returns true if there are no elements // on the stack; false otherwise { return ( topPtr == NULL ); } 19

  20. Push( ) • Allocate space for new item • Put new item into the allocated space • Put the allocated space into the stack

  21. 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. 21

  22. ‘X’ ‘C’ ‘L’ topPtr Adding newItem to the stack ‘B’ newItem newItem = ‘B’; NodeType<char>* location; location = new NodeType<char>; location->info = newItem; location->next = topPtr; topPtr = location;

  23. ‘X’ ‘C’ ‘L’ topPtr Adding newItem to the stack ‘B’ newItem newItem = ‘B’; NodeType<char>* location; location = new NodeType<char>; location->info = newItem; location->next = topPtr; topPtr = location; location

  24. ‘X’ ‘C’ ‘L’ topPtr Adding newItem to the stack ‘B’ newItem newItem = ‘B’; NodeType<char>* location; location = new NodeType<char>; location->info = newItem; location->next = topPtr; topPtr = location; location

  25. ‘X’ ‘C’ ‘L’ topPtr Adding newItem to the stack ‘B’ newItem newItem = ‘B’; NodeType<char>* location; location = new NodeType<char>; location->info = newItem; location->next = topPtr; topPtr = location; ‘B’ location

  26. ‘X’ ‘C’ ‘L’ topPtr Adding newItem to the stack ‘B’ newItem newItem = ‘B’; NodeType<char>* location; location = new NodeType<char>; location->info = newItem; location->next = topPtr; topPtr = location; ‘B’ location

  27. topPtr Adding newItem to the stack ‘B’ newItem newItem = ‘B’; NodeType<char>* location; location = new NodeType<char>; location->info = newItem; location->next = topPtr; topPtr = location; ‘X’ ‘C’ ‘L’ ‘B’ location

  28. Implementing Push template<class ItemType> void StackType<ItemType>::Push ( ItemType newItem ) // Adds newItem to the top of the stack. { NodeType<ItemType>* location; location = new NodeType<ItemType>; location->info = newItem; location->next = topPtr; topPtr = location; } 28

  29. Pop( ) • Set item to Info (top node) • Unlink the top node from the stack • Deallocate the old top node

  30. Using operator delete The object currently pointed to by the pointer is deallocated, and the pointer is considered unassigned. The memory is returned to the free store. 30

  31. topPtr Deleting item from the stack item NodeType<ItemType>* tempPtr; item = topPtr->info; tempPtr = topPtr; topPtr = topPtr->next; delete tempPtr; ‘B’ ‘X’ ‘C’ ‘L’ tempPtr

  32. topPtr Deleting item from the stack ‘B’ item NodeType<ItemType>* tempPtr; item = topPtr->info; tempPtr = topPtr; topPtr = topPtr->next; delete tempPtr; ‘B’ ‘X’ ‘C’ ‘L’ tempPtr

  33. topPtr Deleting item from the stack ‘B’ item NodeType<ItemType>* tempPtr; item = topPtr->info; tempPtr = topPtr; topPtr = topPtr->next; delete tempPtr; ‘B’ ‘X’ ‘C’ ‘L’ tempPtr

  34. topPtr Deleting item from the stack ‘B’ item NodeType<ItemType>* tempPtr; item = topPtr->info; tempPtr = topPtr; topPtr = topPtr->next; delete tempPtr; ‘B’ ‘X’ ‘C’ ‘L’ tempPtr

  35. topPtr Deleting item from the stack ‘B’ item NodeType<ItemType>* tempPtr; item = topPtr->info; tempPtr = topPtr; topPtr = topPtr->next; delete tempPtr; ‘X’ ‘C’ ‘L’ tempPtr

  36. Implementing Pop template<class ItemType> void StackType<ItemType>::Pop ( ItemType& item ) // Removes element at the top of the stack and // returns it in item. { NodeType<ItemType>* tempPtr; item = topPtr->info; tempPtr = topPtr; topPtr = topPtr->next; delete tempPtr; } 36

  37. template<class ItemType> bool StackType<ItemType>::IsFull( ) const // Returns true if there is no room for // another NodeType node on the free store; // false otherwise. { location = new NodeType<ItemType>; if ( location == NULL ) return true; else { delete location; return false; } } 37

  38. Why is a destructor needed? When a local stack variable goes out of scope, the memory space for data member topPtr is deallocated. But the nodes that topPtr points to are not automatically deallocated. A class destructor is used to deallocate the dynamic memory pointed to by the data member.

  39. template<class ItemType> void StackType<ItemType>::MakeEmpty( ) // Post: Stack is empty; all elements deallocated. { NodeType<ItemType>* tempPtr;; while ( topPtr != NULL ) { tempPtr = topPtr; topPtr = topPtr->next; delete tempPtr; } } template<class ItemType> StackType<ItemType>::~StackType( ) // destructor { MakeEmpty( ); } 39

  40. What is a Queue? • Logical (or ADT) level:A queue is an ordered group of homogeneous items (elements), in which new elements are added at one end (the rear), and elements are removed from the other end (the front). • A queue is a FIFO “first in, first out” structure.

  41. Queue ADT Operations • MakeEmpty -- Sets queue to an empty state. • IsEmpty -- Determines whether the queue is currently empty. • IsFull -- Determines whether the queue is currently full. • Enqueue (ItemType newItem) -- Adds newItem to the rear of the queue. • Dequeue (ItemType& item) -- Removes the item at the front of the queue and returns it in item. 41

  42. ADT Queue Operations Transformers • MakeEmpty • Enqueue • Dequeue Observers • IsEmpty • IsFull change state observe state 42

  43. ‘C’ ‘Z’ ‘T’ class QueType<char> QueType Private Data: qFront qRear ~QueType Enqueue Dequeue . . .

  44. // DYNAMICALLY LINKED IMPLEMENTATION OF QUEUE #include "ItemType.h" // for ItemType template<class ItemType> class QueType { public: QueType( ); // CONSTRUCTOR ~QueType( ) ; // DESTRUCTOR bool IsEmpty( ) const; bool IsFull( ) const; void Enqueue( ItemType item ); void Dequeue( ItemType& item ); void MakeEmpty( ); private: NodeType<ItemType>* qFront; NodeType<ItemType>* qRear; }; 44

  45. // DYNAMICALLY LINKED IMPLEMENTATION OF QUEUE continued // member function definitions for class QueType template<class ItemType> QueType<ItemType>::QueType( ) // CONSTRUCTOR { qFront = NULL; qRear = NULL; } template<class ItemType> bool QueType<ItemType>::IsEmpty( ) const { return ( qFront == NULL ) } 45

  46. template<class ItemType> void QueType<ItemType>::Enqueue( ItemType newItem ) // Adds newItem to the rear of the queue. // Pre: Queue has been initialized. // Queue is not full. // Post: newItem is at rear of queue. { NodeType<ItemType>* ptr; ptr = new NodeType<ItemType>; ptr->info = newItem; ptr->next = NULL; if ( qRear == NULL ) qFront = ptr; else qRear->next = ptr; qRear = ptr; } 46

  47. template<class ItemType> void QueType<ItemType>::Dequeue( ItemType& item ) // Removes element from from front of queue // and returns it in item. // Pre: Queue has been initialized. // Queue is not empty. // Post: Front element has been removed from queue. // item is a copy of removed element. { NodeType<ItemType>* tempPtr; tempPtr = qFront; item = qFront->info; qFront = qFornt->next; if ( qFront == NULL ) qRear = NULL; delete tempPtr; } 47

  48. What is a List? • A list is a homogeneous collection of elements, with a linear relationship between elements. • That is, each list element (except the first) has a unique predecessor, and each element (except the last) has a unique successor.

  49. Implementing the Unsorted List as a Linked Structure

  50. change state observe state process all ADT Unsorted List Operations Transformers • MakeEmpty • InsertItem • DeleteItem Observers • IsFull • LengthIs • RetrieveItem Iterators • ResetList • GetNextItem 50

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