Data Structures - Lecture 9 [Stack & Queue using Linked List]
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This document discusses implementing stacks and queues using linked lists. For a stack, elements are inserted and removed from the head (start) of the linked list for constant time operations. For a queue, elements are inserted at the head and removed from the tail (end) of the linked list, requiring traversing to the second last node for removal. Implementing stacks and queues with linked lists avoids size limitations of arrays and uses dynamic memory allocation.
Data Structures - Lecture 9 [Stack & Queue using Linked List]
- 1. Stack & Queue Using Linked List INSTRUCTOR : MUHAMMAD HAMMAD WASEEM EMAIL: [email protected]
- 2. Stack Using Linked List We can avoid the size limitation of a stack implemented with an array by using a linked list to hold the stack elements. As with array, however, we need to decide where to insert elements in the list and where to delete them so that push and pop will run the fastest. 2
- 3. Stack Using Linked List For a singly-linked list, insert at start or end takes constant time using the head and current pointers respectively. Removing an element at the start is constant time but removal at the end required traversing the list to the node one before the last. Make sense to place stack elements at the start of the list because insert and removal are constant time. 3
- 4. Stack Using Linked List No need for the current pointer; head is enough. 4 top 2 5 7 1 1 7 5 2 head
- 5. Stack Operation: List int pop() { int x = head->info; head = head->link; return x; } 5 top 2 5 7 1 7 5 2 head
- 6. Stack Operation: List void push(int x) { ListNode *newNode; newNode = new ListNode; newNode->info = x; newNode->link=head; head = newNode; } 6 top 2 5 7 9 7 5 2 head push(9) 9 newNode
- 7. Stack Operation: List int top() { return head->info; } int IsEmpty() { return ( head == NULL ); } All operations take constant time. 7
- 8. Stack: Array or List Since both implementations support stack operations in constant time, any reason to choose one over the other? Allocating and de-allocating memory for list nodes does take more time than pre-allocated array. List uses only as much memory as required by the nodes; array requires allocation ahead of time. List pointers (head, next) require extra memory. Array has an upper limit; List is limited by dynamic memory allocation. 8
- 9. Queue Using Linked List Insert an element at the start and removal at the end but it required extra overhead of traversing the list to the node one before the last. 9
- 10. Queue Using Linked List No need for the current pointer; head is enough. 10 rear 2571 1 7 5 2 rear front front
- 11. Queue Operation: enqueue void enqueue(int x) { ListNode *newNode; newNode = new ListNode; newNode->info = x; newNode->link=head; head = newNode; } 11
- 12. Queue Operation: dequeue Void dequeue() { nodePtr = head; while (nodePtr->link != NULL) { previousNode = nodePtr; nodePtr = nodePtr->next; } previousNode->link = nodePtr->link; delete nodePtr; } 12