Implement a stack using singly linked list (original) (raw)

Last Updated : 20 Mar, 2025

Try it on GfG Practice

To implement a stack using a singly linked list, we need to ensure that all operations follow the **LIFO (Last In, First Out) principle. This means that the most recently added element is always the first one to be removed. In this approach, we use a singly linked list, where each node contains data and a reference (or link) to the next node.

To manage the stack, we maintain a top pointer that always points to the most recent (topmost) node in the stack. The key stack operations—push, pop, and peek can be performed using this top pointer.

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

C++ `

#include <bits/stdc++.h> using namespace std;

class Node { public: int data; Node* next; Node(int new_data) { this->data = new_data; this->next = nullptr; } };

class Stack { Node* head;

public: Stack() { this->head = nullptr; }

bool isEmpty() {
    return head == nullptr;
}

void push(int new_data) {
    Node* new_node = new Node(new_data);
    if (!new_node) {
        cout << "\nStack Overflow";
    }
    new_node->next = head;
    head = new_node;
}

void pop() {
    if (this->isEmpty()) {
        cout << "\nStack Underflow" << endl;
    } else {
        Node* temp = head;
        head = head->next;
        delete temp;
    }
}

int peek() {
    if (!isEmpty())
        return head->data;
    else {
        cout << "\nStack is empty";
        return INT_MIN;
    }
}

};

int main() { Stack st;

st.push(11);
st.push(22);
st.push(33);
st.push(44);

cout << "Top element is " << st.peek() << endl;

cout << "Removing two elements..." << endl;
st.pop();
st.pop();

cout << "Top element is " << st.peek() << endl;

return 0;

}

C

// 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

// 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());
}

}

Python

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#

// 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

// 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());

`

Output

Top element is 44 Removing two elements... 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.
**Auxiliary Space: O(n), where n is the size of the stack

Benefits of implementing a stack using a singly linked list

• **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.

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, its return address and parameters are pushed onto the stack. The stack ensures functions execute and return in reverse order..
• **Undo/Redo Operations: In apps like text or image editors, actions are pushed onto a stack. Undo removes the last action, while redo restores it.
• **Browser History: Browsers use stacks to track visited pages. Visiting a page pushes its URL onto the stack, and the "Back" button pops the last URL to go to the previous page.
• **Expression Evaluation: In compilers, expressions are converted to postfix notation and evaluated using a stack.
• **Call Stack in Recursion: Recursive function calls are pushed onto the stack. Once recursion ends, the stack is popped to return to the previous function call.