Implement a stack using singly linked list

To implement a stack using the singly linked list concept, all the singly linked list operations should be performed based on Stack operations LIFO(last in first out) and with the help of that knowledge, we are going to implement a stack using a singly linked list. 

So we need to follow a simple rule in the implementation of a stack which is last in first out and all the operations can be performed with the help of a top variable. Let us learn how to perform Pop, Push, Peek, and Display operations in the following article:

In the stack Implementation, a stack contains a top pointer. which is the “head” of the stack where pushing and popping items happens at the head of the list. The first node has a null in the link field and second node-link has the first node address in the link field and so on and the last node address is in the “top” pointer.

The main advantage of using a linked list over arrays is that it is possible to implement a stack that can shrink or grow as much as needed. Using an array will put a restriction on the maximum capacity of the array which can lead to stack overflow. Here each new node will be dynamically allocated. so overflow is not possible.

Stack Operations: 

• push(): Insert a new element into the stack i.e just insert a new element at the beginning of the linked list.
• pop(): Return the top element of the Stack i.e simply delete the first element from the linked list.
• peek(): Return the top element.
• display(): Print all elements in Stack.

Push Operation:

• Initialise a node
• Update the value of that node by data i.e. node->data = data
• Now link this node to the top of the linked list
• And update top pointer to the current node

Pop Operation:

• First Check whether there is any node present in the linked list or not, if not then return
• Otherwise make pointer let say temp to the top node and move forward the top node by 1 step
• Now free this temp node

Peek Operation:

• Check if there is any node present or not, if not then return.
• Otherwise return the value of top node of the linked list

Display Operation:

• Take a temp node and initialize it with top pointer 
• Now start traversing temp till it encounters NULL
• Simultaneously print the value of the temp node

Below is the implementation of the above operations 

// C++ program to implement a stack using singly linked list
#include <bits/stdc++.h>
using namespace std;

// Class representing a node in the linked list
class Node {
public:
    int data;
    Node* next;
    Node(int new_data) {
        this->data = new_data;
        this->next = nullptr;
    }
};

// Class to implement stack using a singly linked list
class Stack {

    // head of the linked list
    Node* head;

public:
    // Constructor to initialize the stack
    Stack() { this->head = nullptr; }

    // Function to check if the stack is empty
    bool isEmpty() {
      
        // If head is nullptr, the stack is empty
        return head == nullptr;
    }

    // Function to push an element onto the stack
    void push(int new_data) {
      
        // Create a new node with given data
        Node* new_node = new Node(new_data);

        // Check if memory allocation for the new node
        // failed
        if (!new_node) {
            cout << "\nStack Overflow";
        }

        // Link the new node to the current top node
        new_node->next = head;

        // Update the top to the new node
        head = new_node;
    }

    // Function to remove the top element from the stack
    void pop() {

        // Check for stack underflow
        if (this->isEmpty()) {
            cout << "\nStack Underflow" << endl;
        }
        else {
            // Assign the current top to a temporary
            // variable
            Node* temp = head;

            // Update the top to the next node
            head = head->next;

            // Deallocate the memory of the old top node
            delete temp;
        }
    }

    // Function to return the top element of the stack
    int peek() {

        // If stack is not empty, return the top element
        if (!isEmpty())
            return head->data;
        else {
            cout << "\nStack is empty";
            return INT_MIN;
        }
    }
};

// Driver program to test the stack implementation
int main() {
    // Creating a stack
    Stack st;

    // Push elements onto the stack
    st.push(11);
    st.push(22);
    st.push(33);
    st.push(44);

    // Print top element of the stack
    cout << "Top element is " << st.peek() << endl;

    // removing two elemements from the top
      cout << "Removing two elements..." << endl;
    st.pop();
    st.pop();

    // Print top element of the stack
    cout << "Top element is " << st.peek() << endl;

    return 0;
}

// C program to implement a stack using singly linked list
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>

// Struct representing a node in the linked list
typedef struct Node {
    int data;
    struct Node* next;
} Node;
Node* createNode(int new_data) {
    Node* new_node = (Node*)malloc(sizeof(Node));
    new_node->data = new_data;
    new_node->next = NULL;
    return new_node;
}

// Struct to implement stack using a singly linked list
typedef struct Stack {
    Node* head;
} Stack;

// Constructor to initialize the stack
void initializeStack(Stack* stack) { stack->head = NULL; }

// Function to check if the stack is empty
int isEmpty(Stack* stack) {
  
    // If head is NULL, the stack is empty
    return stack->head == NULL;
}

// Function to push an element onto the stack
void push(Stack* stack, int new_data) {
  
    // Create a new node with given data
    Node* new_node = createNode(new_data);

    // Check if memory allocation for the new node failed
    if (!new_node) {
        printf("\nStack Overflow");
        return;
    }

    // Link the new node to the current top node
    new_node->next = stack->head;

    // Update the top to the new node
    stack->head = new_node;
}

// Function to remove the top element from the stack
void pop(Stack* stack) {
  
    // Check for stack underflow
    if (isEmpty(stack)) {
        printf("\nStack Underflow\n");
        return;
    }
    else {
      
        // Assign the current top to a temporary variable
        Node* temp = stack->head;

        // Update the top to the next node
        stack->head = stack->head->next;

        // Deallocate the memory of the old top node
        free(temp);
    }
}

// Function to return the top element of the stack
int peek(Stack* stack) {
  
    // If stack is not empty, return the top element
    if (!isEmpty(stack))
        return stack->head->data;
    else {
        printf("\nStack is empty");
        return INT_MIN;
    }
}

// Driver program to test the stack implementation
int main() {
  
    // Creating a stack
    Stack stack;
    initializeStack(&stack);

    // Push elements onto the stack
    push(&stack, 11);
    push(&stack, 22);
    push(&stack, 33);
    push(&stack, 44);

    // Print top element of the stack
    printf("Top element is %d\n", peek(&stack));

  
      // removing two elemements from the top
      printf("Removing two elements...\n");
    pop(&stack);
    pop(&stack);

    // Print top element of the stack
    printf("Top element is %d\n", peek(&stack));

    return 0;
}

// Java program to implement a stack using singly linked
// list

// Class representing a node in the linked list
class Node {
    int data;
    Node next;
    Node(int new_data) {
        this.data = new_data;
        this.next = null;
    }
}

// Class to implement stack using a singly linked list
class Stack {

    // Head of the linked list
    Node head;

    // Constructor to initialize the stack
    Stack() { this.head = null; }

    // Function to check if the stack is empty
    boolean isEmpty() {
      
        // If head is null, the stack is empty
        return head == null;
    }

    // Function to push an element onto the stack
    void push(int new_data) {
      
        // Create a new node with given data
        Node new_node = new Node(new_data);

        // Check if memory allocation for the new node
        // failed
        if (new_node == null) {
            System.out.println("\nStack Overflow");
            return;
        }

        // Link the new node to the current top node
        new_node.next = head;

        // Update the top to the new node
        head = new_node;
    }

    // Function to remove the top element from the stack
    void pop() {
      
        // Check for stack underflow
        if (isEmpty()) {
            System.out.println("\nStack Underflow");
            return;
        }
        else {
          
            // Assign the current top to a temporary
            // variable
            Node temp = head;

            // Update the top to the next node
            head = head.next;

            // Deallocate the memory of the old top node
            temp = null;
        }
    }

    // Function to return the top element of the stack
    int peek() {
      
        // If stack is not empty, return the top element
        if (!isEmpty())
            return head.data;
        else {
            System.out.println("\nStack is empty");
            return Integer.MIN_VALUE;
        }
    }
}

// Driver code
public class Main {
    public static void main(String[] args)
    {
        // Creating a stack
        Stack st = new Stack();

        // Push elements onto the stack
        st.push(11);
        st.push(22);
        st.push(33);
        st.push(44);

        // Print top element of the stack
        System.out.println("Top element is " + st.peek());

        // removing two elemements from the top
          System.out.println("Removing two elements...");
        st.pop();
        st.pop();

        // Print top element of the stack
        System.out.println("Top element is " + st.peek());
    }
}

# Java program to implement a stack using singly linked
# list

# Class representing a node in the linked list
class Node:
    def __init__(self, new_data):
        self.data = new_data
        self.next = None

# Class to implement stack using a singly linked list
class Stack:
    def __init__(self):

        # head of the linked list
        self.head = None

    # Function to check if the stack is empty
    def is_empty(self):

        # If head is None, the stack is empty
        return self.head is None

    # Function to push an element onto the stack
    def push(self, new_data):

        # Create a new node with given data
        new_node = Node(new_data)

        # Check if memory allocation for the new node failed
        if not new_node:
            print("\nStack Overflow")
            return

        # Link the new node to the current top node
        new_node.next = self.head

        # Update the top to the new node
        self.head = new_node

    # Function to remove the top element from the stack
    def pop(self):

        # Check for stack underflow
        if self.is_empty():
            print("\nStack Underflow")
        else:

            # Assign the current top to a temporary variable
            temp = self.head

            # Update the top to the next node
            self.head = self.head.next

            # Deallocate the memory of the old top node
            del temp

    # Function to return the top element of the stack
    def peek(self):

        # If stack is not empty, return the top element
        if not self.is_empty():
            return self.head.data
        else:
            print("\nStack is empty")
            return float('-inf')


# Creating a stack
st = Stack()

# Push elements onto the stack
st.push(11)
st.push(22)
st.push(33)
st.push(44)

# Print top element of the stack
print("Top element is", st.peek())

# removing two elemements from the top
print("Removing two elements...");
st.pop()
st.pop()

# Print top element of the stack
print("Top element is", st.peek())

// C# program to implement a stack using singly linked list
using System;

// Class representing a node in the linked list
class Node {
    public int data;
    public Node next;
    public Node(int new_data)
    {
        this.data = new_data;
        this.next = null;
    }
}

// Class to implement stack using a singly linked list
class Stack {

    // head of the linked list
    private Node head;

    // Constructor to initialize the stack
    public Stack() { this.head = null; }

    // Function to check if the stack is empty
    public bool isEmpty()
    {

        // If head is null, the stack is empty
        return head == null;
    }

    // Function to push an element onto the stack
    public void push(int new_data)
    {

        // Create a new node with given data
        Node new_node = new Node(new_data);

        // Check if memory allocation for the new node
        // failed
        if (new_node == null) {
            Console.WriteLine("\nStack Overflow");
            return;
        }

        // Link the new node to the current top node
        new_node.next = head;

        // Update the top to the new node
        head = new_node;
    }

    // Function to remove the top element from the stack
    public void pop()
    {

        // Check for stack underflow
        if (this.isEmpty()) {
            Console.WriteLine("\nStack Underflow");
        }
        else {

            // Update the top to the next node
            head = head.next;
            /* No need to manually free the memory of the
             * old head in C# */
        }
    }

    // Function to return the top element of the stack
    public int peek()
    {

        // If stack is not empty, return the top element
        if (!isEmpty())
            return head.data;
        else {
            Console.WriteLine("\nStack is empty");
            return int.MinValue;
        }
    }
}

// Driver program to test the stack implementation
class GfG {
    static void Main(string[] args)
    {

        // Creating a stack
        Stack st = new Stack();

        // Push elements onto the stack
        st.push(11);
        st.push(22);
        st.push(33);
        st.push(44);

        // Print top element of the stack
        Console.WriteLine("Top element is " + st.peek());

        // removing two elemements from the top
          Console.WriteLine("Removing two elements...");
        st.pop();
        st.pop();

        // Print top element of the stack
        Console.WriteLine("Top element is " + st.peek());
    }
}

// Javascript program to implement a stack using singly
// linked list

// Class representing a node in the linked list
class Node {
    constructor(new_data) {
        this.data = new_data;
        this.next = null;
    }
}

// Class to implement stack using a singly linked list
class Stack {

    // Constructor to initialize the stack
    constructor() { this.head = null; }

    // Function to check if the stack is empty
    isEmpty() {
    
        // If head is null, the stack is empty
        return this.head === null;
    }

    // Function to push an element onto the stack
    push(new_data) {
    
        // Create a new node with given data
        const new_node = new Node(new_data);

        // Check if memory allocation for the new node
        // failed
        if (!new_node) {
            console.log("\nStack Overflow");
            return;
        }

        // Link the new node to the current top node
        new_node.next = this.head;

        // Update the top to the new node
        this.head = new_node;
    }

    // Function to remove the top element from the stack
    pop() {
    
        // Check for stack underflow
        if (this.isEmpty()) {
            console.log("\nStack Underflow");
        }
        else {
        
            // Assign the current top to a temporary
            // variable
            let temp = this.head;

            // Update the top to the next node
            this.head = this.head.next;

            // Deallocate the memory of the old top node
            temp = null;
        }
    }

    // Function to return the top element of the stack
    peek() {
    
        // If stack is not empty, return the top element
        if (!this.isEmpty())
            return this.head.data;
        else {
            console.log("\nStack is empty");
            return Number.MIN_VALUE;
        }
    }
}

// Driver program to test the stack implementation
const st = new Stack();

// Push elements onto the stack
st.push(11);
st.push(22);
st.push(33);
st.push(44);

// Print top element of the stack
console.log("Top element is " + st.peek());

// removing two elemements from the top
console.log("Removing two elements...");
st.pop();
st.pop();

// Print top element of the stack
console.log("Top element is " + st.peek());

Top element is 44
Top element is 22

Time Complexity: O(1), for all push(), pop(), and peek(), as we are not performing any kind of traversal over the list. We perform all the operations through the current pointer only.
Auxiliary Space: O(N), where N is the size of the stack

In this implementation, we define a Node class that represents a node in the linked list, and a Stack class that uses this node class to implement the stack. The head attribute of the Stack class points to the top of the stack (i.e., the first node in the linked list).

To push an item onto the stack, we create a new node with the given item and set its next pointer to the current head of the stack. We then set the head of the stack to the new node, effectively making it the new top of the stack.

To pop an item from the stack, we simply remove the first node from the linked list by setting the head of the stack to the next node in the list (i.e., the node pointed to by the next pointer of the current head). We return the data stored in the original head node, which is the item that was removed from the top of the stack.

Benefits of implementing a stack using a singly linked list include:

Dynamic memory allocation: The size of the stack can be increased or decreased dynamically by adding or removing nodes from the linked list, without the need to allocate a fixed amount of memory for the stack upfront.

Efficient memory usage: Since nodes in a singly linked list only have a next pointer and not a prev pointer, they use less memory than nodes in a doubly linked list.

Easy implementation: Implementing a stack using a singly linked list is straightforward and can be done using just a few lines of code.

Versatile: Singly linked lists can be used to implement other data structures such as queues, linked lists, and trees.

In summary, implementing a stack using a singly linked list is a simple and efficient way to create a dynamic stack data structure in Python.

Real time examples of stack:

Stacks are used in various real-world scenarios where a last-in, first-out (LIFO) data structure is required. Here are some examples of real-time applications of stacks:

Function call stack: When a function is called in a program, the return address and all the function parameters are pushed onto the function call stack. The stack allows the function to execute and return to the caller function in the reverse order in which they were called.

Undo/Redo operations: In many applications, such as text editors, image editors, or web browsers, the undo and redo functionalities are implemented using a stack. Every time an action is performed, it is pushed onto the stack. When the user wants to undo the last action, the top element of the stack is popped and the action is reversed.

Browser history: Web browsers use stacks to keep track of the pages visited by the user. Every time a new page is visited, its URL is pushed onto the stack. When the user clicks the “Back” button, the last visited URL is popped from the stack and the user is directed to the previous page.

Expression evaluation: Stacks are used in compilers and interpreters to evaluate expressions. When an expression is parsed, it is converted into postfix notation and pushed onto a stack. The postfix expression is then evaluated using the stack.

Call stack in recursion: When a recursive function is called, its call is pushed onto the stack. The function executes and calls itself, and each subsequent call is pushed onto the stack. When the recursion ends, the stack is popped, and the program returns to the previous function call.

In summary, stacks are widely used in many applications where LIFO functionality is required, such as function calls, undo/redo operations, browser history, expression evaluation, and recursive function calls.

R

Rajput-Ji

Follow

Improve

Article Tags :

• DSA
• Linked List
• Stack
• Technical Scripter
• Technical Scripter 2018

+1 More

Practice Tags :

• Linked List
• Stack