CMSC 341. Deques, Stacks and Queues 9/22/04 1

Size: px

Start display at page:

Download "CMSC 341. Deques, Stacks and Queues 9/22/04 1"

Irene Carpenter
5 years ago
Views:

1 CMSC 341 Deques, Stacks and Queues 9/22/04 1

2 The Double-Ended Queue ADT The double ended queue is referred to as a Deque (rhymes with check ) Restricted List add to the end remove from the end add to the front remove from the front Stacks and Queues are often implemented using a Deque 9/22/04 2

3 insertatfront removefromback removefromfront insertatback 9/22/04 3

4 Front Back 9/22/04 4

5 insertatfront(10) 10 Front Back 9/22/04 5

6 insertatfront(5) 5 10 Front Back 9/22/04 6

7 insertatback(20) Front Back 9/22/04 7

8 insertatback(removefromfront()) Front Back 9/22/04 8

9 Adapting Lists to Implement Deques List interface (Weiss) Does not directly support Deque operations Could support them with a little extra code Any good list interface will support Deque operations Adapter Design Pattern Allow a client to use a class whose interface is different from the one expected by the client Do not modify client or class, write adapter class that sits between them 9/22/04 9

10 Client thedeque.insertatfront(10) Deque (adapter) thelist.insert(10, thelist.zeroth()) List (adaptee) 9/22/04 10

11 Deque.H #include LinkedList.H class Deque public: Deque(); Deque(const Deque &deq); ~Deque(); bool isempty() const; void makeempty(); void insertatfront(const Object &x); void insertatback(const Object &x); Object removefromfront(); Object rremovefromback(); const Deque &operator=(const Deque &deq); 9/22/04 11

12 Deque.H (cont) private: ; List<Object> m_thelist; 9/22/04 12

13 New List Methods Assumed to Exist ListItr<Object> last( ) Returns iterator that points to last object in list void remove(listitr<object> itr) Removes the object pointed to by itr What is the state of itr after remove( )? What are the complexity of last( ) and remove( )? Singly linked Doubly linked 9/22/04 13

14 Deque.C Deque<Object>::Deque() // no code Deque<Object>::Deque(const Deque &deq) m_thelist = deq.m_thelist; Deque<Object>::~Deque() // no code 9/22/04 14

15 Deque.C (cont) bool Deque<Object>::isEmpty( ) const return m_thelist.isempty( ); void Deque<Object>::makeEmpty ( ) m_thelist.makeempty(); 9/22/04 15

16 Deque.C (cont) Object Deque<Object>::removeFromFront( ) if (isempty()) throw DequeException( remove on empty deque ); Object tmp = m_thelist.first().retrieve(); m_thelist.remove(m_thelist.first( )); return tmp; void Deque<Object>::insertAtFront(const Object &x) m_thelist.insert(x, m_thelist.zeroth( )); 9/22/04 16

17 Deque.C (cont) Object Deque<Object>::removeFromBack( ) if (isempty()) throw DequeException( remove on empty deque ); Object tmp = m_thelist.last().retrieve(); m_thelist.remove(m_thelist.last( )); return tmp; void Deque<Object>::insertAtBack(const Object &x) m_thelist.insert(x, m_thelist.last( )); 9/22/04 17

18 Deque.C (cont) const Deque<Object> &Deque<Object>:: operator=(const Deque &deq) if (this!= &deq) m_thelist = deq.m_thelist; return *this; 9/22/04 18

19 DequeException.H class DequeException public: DequeException(); // Message is the empty string DequeException(const string & errormsg); DequeException(const DequeException & ce); ~DequeException(); const DequeException & operator=(const DequeException & ce); const string & errormsg() const; // Accessor for msg private: ; string m_msg; 9/22/04 19

20 DequeException.C DequeException::DequeException( ) /* no code */ DequeException::DequeException(const string & errormsg) m_msg = errormsg; DequeException::DequeException(const DequeException &ce) m_msg = ce.errormsg(); DequeException::~DequeException( ) /* no code 9/22/04 20

21 DequeException.C (cont) const DequeException & DequeException::operator=(const DequeException & ce) if (this == &ce) return *this; // don't assign to itself m_msg = ce.errormsg(); return *this; const string & DequeException::errorMsg() const return m_msg; 9/22/04 21

22 TestDeque.C int main () Deque<int> deq; deq.insertatback(1); deq.insertatback(2); printdeque(deq); Deque<int> otherdeq; otherdeq = deq; printdeque(otherdeq); cout << deq.removefromfront() << endl; cout << deq.removefromfront() << endl; 9/22/04 22

23 printdeque(deq); printdeque(otherdeq); TestDeque.C (cont) try deq.removefromfront(); catch (DequeException & e) cout << e.errormsg() << endl; 9/22/04 23

24 Restricted List only add to end only remove from front Queue ADT Examples line waiting for service jobs waiting to print Implement using a Deque 9/22/04 24

25 Queue.H class Queue public: Queue(); ~Queue(); bool isempty() const; void makeempty(); Object dequeue(); void enqueue (const Object & x); private: Deque<Object> m_thedeque; 9/22/04 25

26 Queue.C Queue<Object>::Queue() /* no code */ Queue<Object>::~Queue() /* no code * / void Queue<Object>::makeEmpty( ) m_thedeque.makeempty(); 9/22/04 26

27 Queue.C (cont d) void Queue<Object>::enqueue(const Object &x) m_thedeque.insertatback(x); Object Queue<Object>::dequeue() return m_thedeque.removefromfront( ); 9/22/04 27

28 An Alternative Queue.H class Queue public: Queue(int capacity = 10); ~Queue(); bool isempty() const; void makeempty(); Object dequeue(); void enqueue (const Object & x); private: vector<object> m_thearray; int m_currentsize; int m_front; int m_back; void increment (int &x); 9/22/04 28

29 Queue.C Queue<Object>::Queue( int capacity ) : m_thearray( capacity ) makeempty( ); // make queue logically empty void Queue<Object>::makeEmpty( ) m_currentsize = 0; m_front = 0; m_back = -1; 9/22/04 29

30 Queue.C (cont d) void Queue<Object>::enqueue(const Object &x) if (isfull()) throw Overflow(); increment (m_back); m_thearray[m_back] = x; m_currentsize++; void Queue<Object>::increment(int &x) if (++x == m_thearray.size()) x = 0; 9/22/04 30

31 Queue.C (cont) Object Queue<Object>::dequeue() if (isempty()) throw Underflow(); m_currentsize--; Object frontitem = m_thearray[m_front]; increment(m_front); return frontitem; 9/22/04 31

32 thearray 9/22/04 32

33 Restricted List only add to top only remove from top Stack ADT Examples pile of trays partial results local state Implement using a Deque 9/22/04 33

34 Stack.H class Stack public: Stack( ); ~Stack( ); bool isempty( ) const; void makeempty( ); Object pop(); void push(const Object &x); private: Deque<Object> m_thedeque; ; 9/22/04 34

35 Stack.C Stack<Object>::Stack() /* no code */ Stack<Object>::~Stack() /* no code */ void Stack<Object>::makeEmpty( ) m_thedeque.makeempty(); 9/22/04 35

36 Stack.C (cont d) void Stack<Object>::push(const Object &x) m_thedeque.insertatfront(x); Object Stack<Object>::pop() return m_thedeque.removefromfront( ); 9/22/04 36

CMSC 341 Lecture 7. Announcements. Proj 2 up Project Preview tonight and tomorrow

CMSC 341 Lecture 7. Announcements. Proj 2 up Project Preview tonight and tomorrow CMSC 341 Lecture 7 Announcements Proj 2 up Project Preview tonight and tomorrow 1 Comparing Performance Linear S Linked D Linked Cursor constructor O(1) O(1) O(1) O(1) find O(n) O(n) O(n) O(n) findprev