Stacks & Queues Using Arrays

1. Stacks & QueuesUsing Arrays

2. Stack • A stack is a data structure in which all insertions and deletions of entries are made at one end, called the top of the stack. • The last entry which is inserted is the first one that will be removed. (Last In First Out : LIFO)

3. Application of Stack • Page visited history in a Web-browser • Undo sequence in a text editor • Program run-time environment

4. Pushing and popping a stack • Push box A onto the stack • Push box B onto the stack • Pop a box from the stack • Pop a box from the stack • Push box C onto the stack • Push box D onto the stack • Push box E onto the stack • Push box F onto the stack

5. Implementation of Stack • Some Basic Operations for Stacks • Create a stack, leaving it empty. • Test whether the stack is Empty. • Retrieve the Top entry from the stack, provided the stack is not empty. • Pop the entry of the top of the stack, provided the stack is not empty. • Push a new entry onto the top off the stack, provided that the stack is not full.

6. Basic Operation

7. Basic Operation

8. Basic Operations for Stacks • Create a stack, leaving it empty. • Test whether the stack is Empty. • Test whether the stack is Full. • Return the Size (number of entries) of the stack. • Retrieve the Top entry from the stack, provided the stack is not empty. • Pop the entry off the top of the stack, provided the stack is not empty. • Push a new entry onto the top of the stack, provided that the stack is not full. • Print all the entries of the stack.

9. The Stack Class • Methods: • Stack (constructor) • empty • full • size • top • pop • push • print • Data members

10. Stack Implementation - Array typedef double Stack_entry; const int max = 100; class Stack { public: Stack(); bool empty(); bool full(); int size(); bool top(Stack_entry &item); bool pop(); bool push(Stack_entry item); void print(); private: int count; Stack_entry entry[max]; };

11. Data Structure - Array

12. Create Stack • We use a constructor to initialize a new created stack as empty. Stack::Stack() // O(1) // Initialize Stack to be empty { count = 0; }

13. Empty bool Stack::empty() // A result of true is returned if the Stack // is empty, otherwise false is returned. { return count == 0; }

14. Full bool Stack::full() // A result of true is returned if the Stack // is full, otherwise false is returned. { return count == max; }

15. Size int Stack::size() // return the # of entries in the stack. { return count; }

16. Top bool Stack::top(Stack_entry &item) // The top of a nonempty Stack is copied to // item. A code of underflow is returned if the // Stack is empty. { if(empty()) return false; item = entry[counter-1]; return true; }

17. Pop bool Stack::pop() // If the Stack is not empty, the top of the // Stack is removed. If the Stack is empty, an // Error code of underflow is returned and the // Stack is left unchanged. { if(empty()) return false; count--; return true; }

18. Push bool Stack::push(Stack_entry item) // If the Stack is not full, item is added // to the top of the Stack. If the Stack is full, // an Error code of overflow is returned and the // Stack is left unchanged. { if(full()) return false; entry[count++] = item; return true; }

19. Print void Stack::print() // Display the entries of the Stack. { if (empty()) cout << "Empty stack"; else{ cout << endl << "The Stack is: "; for (int i=count-1; i>=0; i--) cout << entry[i] << " "; } cout << endl; }

20. Queues

21. Queue • A data structure modeled after a line of people waiting to be served. • The first entry which is inserted is the first one that will be removed. (First In First Out : FIFO)

22. The Queue Class • Functions: • Queue (constructor) • clear • empty • full • size • retrieve • dequeue • enqueue • print • Data members

23. Queue Implementation - Array typedef double Queue_entry; const int max = 100; class Queue { public: Queue(); void clear(); bool empty(); bool full(); int size(); bool retrieve(Queue_entry &item); bool dequeue(); bool enqueue(Queue_entry item); void print(); private: int count; Queue_entry entry[max]; };

24. Data Structure - Array

25. Create Queue • We use a constructor to initialize a new created queue as empty. Queue::Queue() // O(1) { count = 0; }

26. Clear Queue::clear() // O(1) { count = 0; }

27. Empty bool Queue::empty() { return count == 0; }

28. Full bool Queue::full() { return count == max; }

29. Size int Queue::size() { return count; }

30. Retrieve bool Queue::retrieve(Queue_entry &item) { if(empty()) return false; item = entry[0]; return true; }

31. Dequeue bool Queue::dequeue() // O(n) { if (empty()) return false; count--; for(int i = 0; i < count; i++) entry[i] = entry[i+1]; return true; }

32. Enqueue bool Queue::enqueue(Queue_entry item) // O(1) { if(full()) return false; entry[count] = item; count++; return true; }

33. Print void Queue::print() { for (int i=0; i<count; i++) cout << entry[i] << " "; }

34. Data Structure – Circular Array

35. Data Structure – Circular Array

36. Circular Queue

37. Create Queue Queue::Queue() { front = 0; rear = -1; }

38. Clear Queue::clear() { rear = -1; }

39. Empty bool Queue::empty() { return rear == -1; }

40. Next int Queue::next(int n) { return ((n+1)==max) ? 0 : (n+1); }

41. Full bool Queue::full() { return (rear!=-1) && (next(rear)==front); }

42. Size int Queue::size() { int s; if (empty()) s = 0; else{ s = rear-front+1; if (front>rear) s = max + s; } return s; }

43. Retrieve bool Queue::retrieve(Queue_entry &item) { if (empty()) return false; item = entry[front]; return true; }

44. Dequeue bool Queue::dequeue() { if (empty()) return false; if (front==rear) // one element rear = -1; else front = next(front); return true; }

45. Enqueue bool Queue::enqueue(Queue_entry item) { if (full()) return false; if (empty()) rear = front; else rear = next(rear); entry[rear] = item; return true; }

46. Print void Queue::print() { if (empty()) cout << "The queue is empty" << endl; else{ cout << endl << "The Queue is: "; int i = front; do{ cout << entry[i] << " "; i = next(i); } while (i != next(rear)); } cout << endl; }