Introduction to the Stack. Stacks and Queues. Stack Operations. Stack illustrated. elements of the same type. Week 9. Gaddis: Chapter 18

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1 Stacks and Queues Week 9 Gaddis: Chapter 18 CS 5301 Spring 2017 Ji Seaman Introduction to the Stack Stack: a data structure that hods a coection of eements of the same type. - The eements are accessed according to LIFO order: ast in, first out - No random access to other eements Exampes: - pates in a cafeteria - banges Operations: Stack Operations Stack iustrated stack.pop() stack.pop() - push: add a vaue onto the top of the stack make sure it s not fu first. - pop: remove (and return) the vaue from the top of the stack make sure it s not empty first. - isfu: true if the stack is currenty fu, i.e.,has no more space to hod additiona eements - isempty: true if the stack currenty contains no eements int item; stack.push(2): stack.push(3); stack.push(5); stack.pop(); //item is 5 stack.pop(); //item is 3 stack.push(10); 3 4

2 Impementing a Stack Cass Array impementations: - fixed size (static) arrays: size doesn t change - dynamic arrays: can resize as needed in push Linked List - grow and shrink in size as needed Tempates - any of the above can be impemented using tempates A static stack cass cass IntStack const static int STACKSIZE = 100; // The stack size int stackarray[stacksize]; // The stack array int top; // Index to the top of the stack pubic: // Constructor IntStack() top = -1; // empty stack ; // Stack operations void push(int); int pop(); boo isfu() const; boo isempty() const; 5 6 A static stack cass: push&pop A static stack cass: functions // Member function push pushes the argument onto * // the stack. * void IntStack::push(int num) assert(!isfu()); top++; stackarray[top] = num; assert wi abort the program if its argument evauates to fase it requires #incude <cassert> // Member function pop pops the vaue at the top * // of the stack off, and returns it. * int IntStack::pop() int num = stackarray[top]; top--; return num; 7 ** // Member function isfu returns true if the stack * // is fu, or fase otherwise. * ** boo IntStack::isFu() const return (top == STACKSIZE - 1); // Member function isempty returns true if the stack * // is empty, or fase otherwise. * boo IntStack::isEmpty() const return (top == -1); 8

3 A Dynamic Stack Cass: Linked List impementation Push and pop from the head of the ist: A Dynamic Stack Cass: Linked List impementation Push and pop from the head of the ist: // Member function push pushes the argument onto * // the stack. * // Member function pop pops the vaue at the top * // of the stack off, and returns it. * void DynIntStack::push(int num) assert(!isfu()); Node *temp=new Node; temp->data = num; //insert at head of ist temp->next = head; head = temp; struct Node ; Node* head; // ptr to top int DynIntStack::pop() int resut = head->data; Node * temp = head; head = head->next; deete temp; return resut; struct Node ; Node* head; // ptr to top 9 10 Introduction to the Queue Queue: a data structure that hods a coection of eements of the same type. - The eements are accessed according to FIFO order: first in, first out - No random access to other eements Exampes: - peope in ine at a theatre box office - restocking perishabe inventory 11 Operations: Queue Operations - enqueue: add a vaue onto the of the queue (the end of the ine) make sure it s not fu first. - dequeue: remove a vaue from the of the queue (the of the ine) Next! make sure it s not empty first. - isfu: true if the queue is currenty fu, i.e.,has no more space to hod additiona eements - isempty: true if the queue currenty contains no eements 12

q.enqueue(2); Queue iustrated q.enqueue(3); q.enqueue(5); q.dequeue(); Note: and are variabes used by the impementation to carry out the operations int item; q.enqueue(2): q.enqueue(3); q.enqueue(5); q.dequeue(); //item is 2 q.

4 q.enqueue(2); Queue iustrated q.enqueue(3); q.enqueue(5); q.dequeue(); Note: and are variabes used by the impementation to carry out the operations int item; q.enqueue(2): q.enqueue(3); q.enqueue(5); q.dequeue(); //item is 2 q.dequeue(); //item is 3 q.enqueue(10); q.dequeue(); q.enqueue(10); 13 Impementing a Queue Cass Same as for Stacks: Array impementations: - fixed size (static) arrays: size doesn t change - dynamic arrays: can resize as needed in enqueue Linked List - grow and shrink in size as needed Tempates - any of the above can be impemented using tempates 14 Impementing a Queue: Array When and indices move in the array: - probem: hits end of array quicky - soution: circuar array : wrap index around to of array q.enqueue(3): q.enqueue(4): Impementing a Queue: Array To wrap the index back to the of the array, you can use this code to increment during enqueue: if ( == queuesize-1) = 0; ese = +1; The foowing code is equivaent, but shorter (assuming 0 <= < queuesize): = ( + 1) % queuesize; Do the same for advancing the index. 16

5 t: t: Impementing a Queue: Array When is it fu? When is it empty? one eement eft: no eements eft, passes : (+1)%queueSize== 1 Don t use and to determine if the queue is fu or empty!! (+1)%queueSize== 17 A static queue cass cass IntQueue const static int QUEUESIZE = 100; // capacity of queue int queuearray[queuesize]; // The queue array int ; // Subscript of the queue int ; // Subscript of the queue int numitems; // Number of items in the queue pubic: // Constructor IntQueue() = 0; = -1; numitems = 0; ; // Queue operations void enqueue(int); int dequeue(); boo isempty() const; boo isfu() const; 18 A static queue: enqueue/dequeue A static queue cass: functions // Enqueue inserts a vaue at the of the queue. * void IntQueue::enqueue(int num) assert(!isfu()); = ( + 1) % QUEUESIZE; queuearray[] = num; numitems++; // Dequeue removes the vaue at the of the * // queue and returns the vaue. * int IntQueue::dequeue() // isempty returns true if the queue is empty * boo IntQueue::isEmpty() const return (numitems == 0); // isfu returns true if the queue is fu * boo IntQueue::isFu() const return (numitems == QUEUESIZE); int resut = queuearray[]; = ( + 1) % QUEUESIZE; numitems--; return resut; 19 20

6 A Dynamic Queue Cass: Linked List impementation Use pointers and to point to first and ast eements of the ist: NULL A Dynamic Queue Cass: Linked List impementation Enqueue at the of the ist, dequeue from the : // Enqueue inserts a vaue at the of the queue. * void DynIntQueue::enqueue(int num) assert(!isfu()); Node *temp=new Node; temp->data = num; temp->next = NULL; struct Node ; Node* ; // ptr to first Node* ; // ptr to ast 21 //append to of ist, reset if (isempty()) = = temp; ese ->next = temp; = temp; 22 A Dynamic Queue Cass: Linked List impementation Enqueue at the of the ist, dequeue from the : // Dequeue removes the vaue at the of the * // queue and returns the vaue. * int DynIntQueue::dequeue() int vaue = ->data; // remove the first node () Node *temp = ; = ->next; deete temp; struct Node ; Node* ; // ptr to first Node* ; // ptr to ast if (==NULL) = NULL; return vaue; 23

Introduction to the Stack. Stacks and Queues. Stack Operations. Stack illustrated. Week 9. elements of the same type.

Introduction to the Stack. Stacks and Queues. Stack Operations. Stack illustrated. Week 9. elements of the same type. Stacks and Queues Week 9 Gaddis: Chapter 18 (8th ed.) Gaddis: Chapter 19 (9th ed.) CS 5301 Fall 2018 Jill Seaman Introduction to the Stack Stack: a data structure that holds a collection of elements of