Stack as we know is a Last In First Out(LIFO) data structure. It has the following operations :
- push: push an element into the stack
- pop: remove the last element added
- top: returns the element at top of the stack
Implementation of Stack using Linked List
Stacks can be easily implemented using a linked list. Stack is a data structure to which a data can be added using the push( ) method and data can be removed from it using the pop( ) method. With Linked list, the push operation can be replaced by the add at front method of linked list and pop operation can be replaced by a function which deletes the front node of the linked list.
In this way our Linked list will virtually become a Stack with push( ) and pop( ) methods.
First we create a class node. This is our Linked list node class which will have data in it and a node pointer to store the address of the next node element.
Then we will define our stack class,
node *front; // points to the head of linked list
front = NULL;
void push(int); //add an element
void pop(); //remove an element
int top(); // return top element
Inserting Data in Stack (Linked List)
In order to insert an element into the stack, we will create a node and place it in front of the list.
void Stack :: push(int d)
node *temp; // creating a new node
temp = new node();
temp->data = d; // setting data to it
// add the node in front of list
if(front == NULL)
temp->next = NULL;
temp->next = front;
front = temp;
Now whenever we will call the push ( ) function a new node will get added to our list in the front, which is exactly how a stack behaves.
Removing Element from Stack (Linked List)
In order to do this, we will simply delete the first node, and make the second node, the head of the list.
void Stack :: pop()
if(front == NULL) // if empty
cout << "UNDERFLOW\n";
// delete the first element
node *temp = front;
front = front->next;
Return Top of Stack (Linked List)
In this, we simply return the data stored in the head of the list.
int Stack :: top()
When we say “Implementing Stack using Linked List”, we mean how we can make a Linked List behave like a Stack, after all they are all logical entities. So for any data structure to act as a Stack, it should have push( ) method to add data on top and pop( ) method to remove data from top. Which is exactly what we did and hence accomplished to make a Linked List behave as a Stack.