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Subtract 1 from a number represented as Linked List

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Given the head of the linked list representing a positive integer, the task is to print the updated linked list after subtracting 1 from it.

Examples:

Input: LL = 1 -> 2 -> 3 -> 4
Output: 1 -> 2 -> 3 -> 3

Input: LL = 1 -> 2
Output: 1 -> 1

 

Approach: The given problem can be solved by using recursion. Follow the steps below to solve the problem:

  • Define a function, say subtractOneUtil(Node *head) that takes the head of the linked list as the arguments and perform the following steps:
    • Base Case: If the head node of the Linked List is NULL, then return -1 from that recursive call.
    • Recursive Call: Recursively call for the next node of the linked list and let the value returned by this recursive call be borrow.
    • If the value of borrow is -1 and the value of the head node is 0, then update the value of the head node to 9 and return -1 from the current recursive call.
    • Otherwise, decrement the value of the head node by 1 and return 0 from the current recursive call.
  • Subtract 1 from the Linked List by calling the above function as subtractOneUtil(head).
  • If the update linked list has leading 0s, then move the head pointer.
  • After completing the above steps, print the updated linked list as the resultant linked list.

Below is the implementation of the above approach:

C++




// C++ program for the above approach
 
#include <bits/stdc++.h>
using namespace std;
 
// Linked list Node
class Node {
public:
    int data;
    Node* next;
};
 
// Function to create a new node with
// the given data
Node* newNode(int data)
{
    // Create a new node
    Node* new_node = new Node;
    new_node->data = data;
    new_node->next = NULL;
 
    // Return the created node
    return new_node;
}
 
// Recursive function to subtract 1
// from the linked list and update
// the node value accordingly
int subtractOneUtil(Node* head)
{
 
    // Base Case
    if (head == NULL)
        return -1;
 
    // Recursively call for the next
    // node of the head
    int borrow = subtractOneUtil(
        head->next);
 
    // If there is a borrow
    if (borrow == -1) {
 
        // If the head data is 0, then
        // update it with 9 and return -1
        if (head->data == 0) {
            head->data = 9;
            return -1;
        }
 
        // Otherwise, decrement head's
        // data by 1 and return 0
        else {
            head->data = head->data - 1;
            return 0;
        }
    }
 
    // Otherwise, return 0
    else {
        return 0;
    }
}
 
// Function to subtract 1 from the given
// Linked List representation of number
Node* subtractOne(Node* head)
{
 
    // Recursively subtract 1 from
    // the Linked List
    subtractOneUtil(head);
 
    // Increment the head pointer
    // if there are any leading zeros
    while (head and head->next
           and head->data == 0) {
        head = head->next;
    }
 
    return head;
}
 
// Function to print a linked list
void printList(Node* node)
{
    // Iterate until node is NULL
    while (node != NULL) {
        cout << node->data;
        node = node->next;
    }
    cout << endl;
}
 
// Driver Code
int main()
{
    Node* head = newNode(1);
    head->next = newNode(0);
    head->next->next = newNode(0);
    head->next->next->next = newNode(0);
 
    cout << "List is ";
    printList(head);
 
    head = subtractOne(head);
 
    cout << "Resultant list is ";
    printList(head);
 
    return 0;
}


Java




// Java program for the above approach
import java.util.*;
 
class GFG{
 
// Linked list Node
static class Node
{
    int data;
    Node next;
};
 
// Function to create a new node with
// the given data
static Node newNode(int data)
{
     
    // Create a new node
    Node new_node = new Node();
    new_node.data = data;
    new_node.next = null;
 
    // Return the created node
    return new_node;
}
 
// Recursive function to subtract 1
// from the linked list and update
// the node value accordingly
static  int subtractOneUtil(Node head)
{
 
    // Base Case
    if (head == null)
        return -1;
 
    // Recursively call for the next
    // node of the head
    int borrow = subtractOneUtil(
        head.next);
 
    // If there is a borrow
    if (borrow == -1)
    {
         
        // If the head data is 0, then
        // update it with 9 and return -1
        if (head.data == 0)
        {
            head.data = 9;
            return -1;
        }
 
        // Otherwise, decrement head's
        // data by 1 and return 0
        else
        {
            head.data = head.data - 1;
            return 0;
        }
    }
 
    // Otherwise, return 0
    else
    {
        return 0;
    }
}
 
// Function to subtract 1 from the given
// Linked List representation of number
static Node subtractOne(Node head)
{
 
    // Recursively subtract 1 from
    // the Linked List
    subtractOneUtil(head);
 
    // Increment the head pointer
    // if there are any leading zeros
    while (head != null && head.next != null &&
           head.data == 0)
    {
        head = head.next;
    }
    return head;
}
 
// Function to print a linked list
static void printList(Node node)
{
     
    // Iterate until node is null
    while (node != null)
    {
        System.out.print(node.data);
        node = node.next;
    }
    System.out.println();
}
 
// Driver Code
public static void main(String[] args)
{
    Node head = newNode(1);
    head.next = newNode(0);
    head.next.next = newNode(0);
    head.next.next.next = newNode(0);
 
    System.out.print("List is ");
    printList(head);
 
    head = subtractOne(head);
 
    System.out.print("Resultant list is ");
    printList(head);
}
}
 
// This code is contributed by 29AjayKumar


Python3




# Python3 program for the above approach
 
# Linked list Node
class Node:
     
    def __init__(self, d):
         
        self.data = d
        self.next = None
 
# Recursive function to subtract 1
# from the linked list and update
# the node value accordingly
def subtractOneUtil(head):
     
    # Base Case
    if (head == None):
        return -1
         
    # Recursively call for the next
    # node of the head
    borrow = subtractOneUtil(head.next)
     
    # If there is a borrow
    if (borrow == -1):
         
        # If the head data is 0, then
        # update it with 9 and return -1
        if (head.data == 0):
            head.data = 9
            return -1
             
        # Otherwise, decrement head's
        # data by 1 and return 0
        else:
            head.data = head.data - 1
            return 0
             
    # Otherwise, return 0
    else:
        return 0
 
# Function to subtract 1 from the given
# Linked List representation of number
def subtractOne(head):
 
    # Recursively subtract 1 from
    # the Linked List
    subtractOneUtil(head)
 
    # Increment the head pointer
    # if there are any leading zeros
    while (head and head.next and
           head.data == 0):
        head = head.next
 
    return head
 
# Function to print a linked list
def printList(node):
     
    # Iterate until node is None
    while (node != None):
        print(node.data, end = "")
        node = node.next
         
    print()
 
# Driver Code
if __name__ == '__main__':
     
    head = Node(1)
    head.next = Node(0)
    head.next.next = Node(0)
    head.next.next.next = Node(0)
 
    print("List is ", end = "")
    printList(head)
 
    head = subtractOne(head)
 
    print("Resultant list is ", end = "")
    printList(head)
 
# This code is contributed by mohit kumar 29


C#




// C# program for the above approach
using System;
 
class GFG{
 
// Linked list Node
class Node
{
    public int data;
    public Node next;
};
 
// Function to create a new node with
// the given data
static Node newNode(int data)
{
     
    // Create a new node
    Node new_node = new Node();
    new_node.data = data;
    new_node.next = null;
 
    // Return the created node
    return new_node;
}
 
// Recursive function to subtract 1
// from the linked list and update
// the node value accordingly
static  int subtractOneUtil(Node head)
{
 
    // Base Case
    if (head == null)
        return -1;
 
    // Recursively call for the next
    // node of the head
    int borrow = subtractOneUtil(
        head.next);
 
    // If there is a borrow
    if (borrow == -1)
    {
         
        // If the head data is 0, then
        // update it with 9 and return -1
        if (head.data == 0)
        {
            head.data = 9;
            return -1;
        }
 
        // Otherwise, decrement head's
        // data by 1 and return 0
        else
        {
            head.data = head.data - 1;
            return 0;
        }
    }
 
    // Otherwise, return 0
    else
    {
        return 0;
    }
}
 
// Function to subtract 1 from the given
// Linked List representation of number
static Node subtractOne(Node head)
{
 
    // Recursively subtract 1 from
    // the Linked List
    subtractOneUtil(head);
 
    // Increment the head pointer
    // if there are any leading zeros
    while (head != null && head.next != null &&
           head.data == 0)
    {
        head = head.next;
    }
    return head;
}
 
// Function to print a linked list
static void printList(Node node)
{
     
    // Iterate until node is null
    while (node != null)
    {
        Console.Write(node.data);
        node = node.next;
    }
    Console.WriteLine();
}
 
// Driver Code
public static void Main()
{
    Node head = newNode(1);
    head.next = newNode(0);
    head.next.next = newNode(0);
    head.next.next.next = newNode(0);
 
    Console.Write("List is ");
    printList(head);
 
    head = subtractOne(head);
 
    Console.Write("Resultant list is ");
    printList(head);
}
}
 
// This code is contributed by SURENDRA_GANGWAR


Javascript




<script>
 
// JavaScript program for the above approach
 
// Linked list Node
class Node
{
    constructor()
    {
        this.next = null;
    }
}
 
// Function to create a new node with
// the given data
function newNode(data)
{
     
    // Create a new node
    let new_node = new Node();
    new_node.data = data;
    new_node.next = null;
 
    // Return the created node
    return new_node;
}
 
// Recursive function to subtract 1
// from the linked list and update
// the node value accordingly
function subtractOneUtil(head)
{
     
    // Base Case
    if (head == null)
        return -1;
 
    // Recursively call for the next
    // node of the head
    let borrow = subtractOneUtil(head.next);
 
    // If there is a borrow
    if (borrow == -1)
    {
         
        // If the head data is 0, then
        // update it with 9 and return -1
        if (head.data == 0)
        {
            head.data = 9;
            return -1;
        }
 
        // Otherwise, decrement head's
        // data by 1 and return 0
        else
        {
            head.data = head.data - 1;
            return 0;
        }
    }
 
    // Otherwise, return 0
    else
    {
        return 0;
    }
}
 
// Function to subtract 1 from the given
// Linked List representation of number
function subtractOne(head)
{
     
    // Recursively subtract 1 from
    // the Linked List
    subtractOneUtil(head);
 
    // Increment the head pointer
    // if there are any leading zeros
    while (head != null && head.next != null &&
           head.data == 0)
    {
        head = head.next;
    }
    return head;
}
 
// Function to print a linked list
function printList(node)
{
     
    // Iterate until node is null
    while (node != null)
    {
        document.write(node.data);
        node = node.next;
    }
    document.write("<br>");
}
 
// Driver Code
let head = newNode(1);
head.next = newNode(0);
head.next.next = newNode(0);
head.next.next.next = newNode(0);
 
document.write("List is ");
printList(head);
 
head = subtractOne(head);
 
document.write("Resultant list is ");
printList(head);
 
// This code is contributed by Dharanendra L V.
 
</script>


Output

List is 1000
Resultant list is 999






Time Complexity: O(N), N is the length of the given linked list.
Auxiliary Space: O(1)

New Approach by reverse the linked list : 

  1. Subtract 1 from the first node (i.e., the ones place), and then handle the carry if require.
  2. .Then, reverse the linked list back to its original form and return the updated linked list.

Below is the implementation of the above approach:

C++




// C++ program for the above approach
 
#include <bits/stdc++.h>
using namespace std;
 
// Linked list Node
class Node {
public:
    int data;
    Node* next;
};
 
// Function to create a new node with
// the given data
Node* newNode(int data)
{
    // Create a new node
    Node* new_node = new Node;
    new_node->data = data;
    new_node->next = NULL;
    // Return the created node
    return new_node;
}
 
// Function to reverse a linked list
Node* reverseList(Node* head)
{
    Node *prev = NULL, *curr = head, *next;
    while (curr != NULL) {
        next = curr->next;
        curr->next = prev;
        prev = curr;
        curr = next;
    }
    return prev;
}
 
// Function to subtract 1 from the given
// Linked List representation of number
Node* subtractOne(Node* head)
{
    // Reverse the linked list
    head = reverseList(head);
    // Subtract 1 from the first node
    head->data -= 1;
 
    // Handle the carry if required
    Node* curr = head;
    while (curr->data < 0) {
        curr->data += 10;
        if (curr->next == NULL) {
            curr->next = newNode(0);
        }
        curr->next->data -= 1;
        curr = curr->next;
    }
 
    // Reverse the linked list back to
    // its original form
    head = reverseList(head);
 
    // Increment the head pointer
    // if there are any leading zeros
    while (head and head->next and head->data == 0) {
        head = head->next;
    }
 
    return head;
}
// Function to print a linked list
void printList(Node* node)
{
    // Iterate until node is NULL
    while (node != NULL) {
        cout << node->data;
        node = node->next;
    }
    cout << endl;
}
 
// Driver Code
int main()
{
    Node* head = newNode(1);
    head->next = newNode(0);
    head->next->next = newNode(0);
    head->next->next->next = newNode(0);
    cout << "List is ";
    printList(head);
 
    head = subtractOne(head);
 
    cout << "Resultant list is ";
    printList(head);
 
    return 0;
}
//This code is contributed by chinmaya121221


Java




public class Main {
  // Linked list Node
  static class Node {
    int data;
    Node next;
  }
 
  // Function to create a new node with
  // the given data
  static Node newNode(int data)
  {
 
    // Create a new node
    Node new_node = new Node();
    new_node.data = data;
    new_node.next = null;
    // Return the created node
    return new_node;
  }
 
  // Function to reverse a linked list
  static Node reverseList(Node head) {
    Node prev = null, curr = head, next;
    while (curr != null) {
      next = curr.next;
      curr.next = prev;
      prev = curr;
      curr = next;
    }
    return prev;
  }
 
  // Function to subtract 1 from the given
  // Linked List representation of number
  static Node subtractOne(Node head) {
    // Reverse the linked list
    head = reverseList(head);
    // Subtract 1 from the first node
    head.data -= 1;
 
    // Handle the carry if required
    Node curr = head;
    while (curr.data < 0) {
      curr.data += 10;
      if (curr.next == null) {
        curr.next = newNode(0);
      }
      curr.next.data -= 1;
      curr = curr.next;
    }
 
    // Reverse the linked list back to
    // its original form
    head = reverseList(head);
 
    // Increment the head pointer
    // if there are any leading zeros
    while (head != null && head.next != null && head.data == 0) {
      head = head.next;
    }
 
    return head;
  }
 
  // Function to print a linked list
  static void printList(Node node) {
    // Iterate until node is NULL
    while (node != null) {
      System.out.print(node.data);
      node = node.next;
    }
    System.out.println();
  }
 
  public static void main(String[] args) {
    Node head = newNode(1);
    head.next = newNode(0);
    head.next.next = newNode(0);
    head.next.next.next = newNode(0);
    System.out.print("List is ");
    printList(head);
 
    head = subtractOne(head);
 
    System.out.print("Resultant list is ");
    printList(head);
  }
}


Python3




# Linked list Node
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None
 
# Function to create a new node with the given data
def newNode(data):
    # Create a new node
    new_node = Node(data)
     
    # Return the created node
    return new_node
 
# Function to reverse a linked list
def reverseList(head):
    prev = None
    curr = head
    next = None
 
    while curr != None:
        next = curr.next
        curr.next = prev
        prev = curr
        curr = next
 
    return prev
 
# Function to subtract 1 from the given
# Linked List representation of number
def subtractOne(head):
    # Reverse the linked list
    head = reverseList(head)
 
    # Subtract 1 from the first node
    head.data -= 1
 
    # Handle the carry if required
    curr = head
 
    while curr.data < 0:
        curr.data += 10
        if curr.next == None:
            curr.next = newNode(0)
        curr.next.data -= 1
        curr = curr.next
 
    # Reverse the linked list back to its original form
    head = reverseList(head)
 
    # Increment the head pointer if there are any leading zeros
    while head and head.next and head.data == 0:
        head = head.next
 
    return head
 
# Function to print a linked list
def printList(node):
    # Iterate until node is NULL
    while node != None:
        print(node.data, end="")
        node = node.next
    print()
 
# Driver Code
head = newNode(1)
head.next = newNode(0)
head.next.next = newNode(0)
head.next.next.next = newNode(0)
 
print("List is ")
printList(head)
 
head = subtractOne(head)
 
print("Resultant list is ")
printList(head)


C#




// C# program for the above approach
using System;
 
// Linked list Node
class Node {
    public int data;
    public Node next;
};
 
// Main class
class MainClass {
    // Function to create a new node with
    // the given data
    static Node newNode(int data)
    {
        // Create a new node
        Node new_node = new Node();
        new_node.data = data;
        new_node.next = null;
        // Return the created node
        return new_node;
    }
 
    // Function to reverse a linked list
    static Node reverseList(Node head)
    {
        Node prev = null, curr = head, next;
        while (curr != null) {
            next = curr.next;
            curr.next = prev;
            prev = curr;
            curr = next;
        }
        return prev;
    }
 
    // Function to subtract 1 from the given
    // Linked List representation of number
    static Node subtractOne(Node head)
    {
        // Reverse the linked list
        head = reverseList(head);
        // Subtract 1 from the first node
        head.data -= 1;
 
        // Handle the carry if required
        Node curr = head;
        while (curr.data < 0) {
            curr.data += 10;
            if (curr.next == null) {
                curr.next = newNode(0);
            }
            curr.next.data -= 1;
            curr = curr.next;
        }
 
        // Reverse the linked list back to
        // its original form
        head = reverseList(head);
 
        // Increment the head pointer
        // if there are any leading zeros
        while (head != null && head.next != null
               && head.data == 0) {
            head = head.next;
        }
 
        return head;
    }
 
    // Function to print a linked list
    static void printList(Node node)
    {
        // Iterate until node is NULL
        while (node != null) {
            Console.Write(node.data);
            node = node.next;
        }
        Console.WriteLine();
    }
 
    // Driver Code
    public static void Main()
    {
        Node head = newNode(1);
        head.next = newNode(0);
        head.next.next = newNode(0);
        head.next.next.next = newNode(0);
        Console.Write("List is ");
        printList(head);
 
        head = subtractOne(head);
 
        Console.Write("Resultant list is ");
        printList(head);
    }
}
 
// This code is contributed by rutikbhosale


Javascript




// Linked list Node
class Node {
    constructor(data) {
        this.data = data;
        this.next = null;
    }
}
 
// Function to create a new node with the given data
function newNode(data)
{
 
    // Create a new node
    let new_node = new Node(data);
     
    // Return the created node
    return new_node;
}
 
// Function to reverse a linked list
function reverseList(head) {
    let prev = null,
        curr = head,
        next;
 
    while (curr != null) {
        next = curr.next;
        curr.next = prev;
        prev = curr;
        curr = next;
    }
 
    return prev;
}
 
// Function to subtract 1 from the given
// Linked List representation of number
function subtractOne(head) {
    // Reverse the linked list
    head = reverseList(head);
 
    // Subtract 1 from the first node
    head.data -= 1;
 
    // Handle the carry if required
    let curr = head;
 
    while (curr.data < 0) {
        curr.data += 10;
        if (curr.next == null) {
            curr.next = newNode(0);
        }
        curr.next.data -= 1;
        curr = curr.next;
    }
 
    // Reverse the linked list back to its original form
    head = reverseList(head);
 
    // Increment the head pointer if there are any leading zeros
    while (head && head.next && head.data == 0) {
        head = head.next;
    }
 
    return head;
}
 
// Function to print a linked list
function printList(node) {
    // Iterate until node is NULL
    while (node != null) {
        process.stdout.write(node.data + "");
        node = node.next;
    }
    console.log();
}
 
// Driver Code
let head = newNode(1);
head.next = newNode(0);
head.next.next = newNode(0);
head.next.next.next = newNode(0);
 
console.log("List is ");
printList(head);
 
head = subtractOne(head);
 
console.log("Resultant list is ");
printList(head);


Output

List is 1000
Resultant list is 999






Time Complexity: O(n), where n is the length of the linked list.
Space Complexity: O(n), where n is the length of the linked list.

Another approach using Stack: 

C++




#include <bits/stdc++.h>
using namespace std;
 
// Linked list Node
class Node {
public:
    int data;
    Node* next;
};
 
// Function to create a new node with
// the given data
Node* newNode(int data)
{
    // Create a new node
    Node* new_node = new Node;
    new_node->data = data;
    new_node->next = NULL;
 
    // Return the created node
    return new_node;
}
 
// Function to subtract 1 from the given
// Linked List representation of number using stack
Node* subtractOne(Node* head)
{
    stack<int> s;
     
    // Traverse the linked list and push values onto the stack
    Node* curr = head;
    while (curr != NULL) {
        s.push(curr->data);
        curr = curr->next;
    }
     
    int borrow = 1;
    Node* new_head = NULL;
     
    // Pop elements from the stack and subtract borrow
    while (!s.empty()) {
        int val = s.top() - borrow;
        borrow = 0;
        if (val < 0) {
            val += 10;
            borrow = 1;
        }
        s.pop();
        Node* new_node = newNode(val);
        new_node->next = new_head;
        new_head = new_node;
    }
     
    // Remove leading zeros
    while (new_head != NULL && new_head->data == 0) {
        Node* temp = new_head;
        new_head = new_head->next;
        delete temp;
    }
     
    return new_head;
}
 
// Function to print a linked list
void printList(Node* node)
{
    // Iterate until node is NULL
    while (node != NULL) {
        cout << node->data;
        node = node->next;
    }
    cout << endl;
}
// Nikunj Sonigara
// Driver Code
int main()
{
    Node* head = newNode(1);
    head->next = newNode(0);
    head->next->next = newNode(0);
    head->next->next->next = newNode(0);
 
    cout << "List is ";
    printList(head);
 
    head = subtractOne(head);
 
    cout << "Resultant list is ";
    printList(head);
 
    return 0;
}


Java




import java.util.Stack;
 
// Linked list Node
class Node {
    int data;
    Node next;
 
    Node(int data)
    {
        this.data = data;
        this.next = null;
    }
}
 
public class Main {
 
    // Function to subtract 1 from the given
    // Linked List representation of number using stack
    static Node subtractOne(Node head)
    {
        Stack<Integer> s = new Stack<>();
 
        // Traverse the linked list and push values onto the
        // stack
        Node curr = head;
        while (curr != null) {
            s.push(curr.data);
            curr = curr.next;
        }
 
        int borrow = 1;
        Node new_head = null;
 
        // Pop elements from the stack and subtract borrow
        while (!s.empty()) {
            int val = s.pop() - borrow;
            borrow = 0;
            if (val < 0) {
                val += 10;
                borrow = 1;
            }
            Node new_node = new Node(val);
            new_node.next = new_head;
            new_head = new_node;
        }
 
        // Remove leading zeros
        while (new_head != null && new_head.data == 0) {
            Node temp = new_head;
            new_head = new_head.next;
            temp = null;
        }
 
        return new_head;
    }
 
    // Function to print a linked list
    static void printList(Node node)
    {
        // Iterate until node is null
        while (node != null) {
            System.out.print(node.data);
            node = node.next;
        }
        System.out.println();
    }
 
    // Driver Code
    public static void main(String[] args)
    {
        Node head = new Node(1);
        head.next = new Node(0);
        head.next.next = new Node(0);
        head.next.next.next = new Node(0);
 
        System.out.print("List is ");
        printList(head);
 
        head = subtractOne(head);
 
        System.out.print("Resultant list is ");
        printList(head);
    }
}


Python




# Linked list Node
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None
 
# Function to create a new node with the given data
 
 
def new_node(data):
    # Create a new node
    new_node = Node(data)
 
    # Return the created node
    return new_node
 
# Function to subtract 1 from the given Linked List representation of number using stack
 
 
def subtract_one(head):
    stack = []
 
    # Traverse the linked list and push values onto the stack
    curr = head
    while curr is not None:
        stack.append(curr.data)
        curr = curr.next
 
    borrow = 1
    new_head = None
 
    # Pop elements from the stack and subtract borrow
    while stack:
        val = stack.pop() - borrow
        borrow = 0
        if val < 0:
            val += 10
            borrow = 1
        new_node = Node(val)
        new_node.next = new_head
        new_head = new_node
 
    # Remove leading zeros
    while new_head is not None and new_head.data == 0:
        temp = new_head
        new_head = new_head.next
        del temp
 
    return new_head
 
# Function to print a linked list
 
 
def print_list(node):
    # Iterate until node is None
    while node is not None:
        print node.data,  # Adding a comma to suppress the newline character
        node = node.next
    print  # Print a newline after the loop
 
 
# Driver Code
if __name__ == "__main__":
    head = new_node(1)
    head.next = new_node(0)
    head.next.next = new_node(0)
    head.next.next.next = new_node(0)
 
    print "List is ",
    print_list(head)
 
    head = subtract_one(head)
 
    print "Resultant list is ",
    print_list(head)
# Contributed by sinudp5vi


C#




using System;
using System.Collections.Generic;
 
// Linked list Node
class Node {
    public int data;
    public Node next;
}
 
class GFG {
    // Function to create a new node with
    // the given data
    static Node NewNode(int data)
    {
        // Create a new node
        Node new_node = new Node();
        new_node.data = data;
        new_node.next = null;
 
        // Return the created node
        return new_node;
    }
 
    // Function to subtract 1 from the given
    // Linked List representation of number using stack
    static Node SubtractOne(Node head)
    {
        Stack<int> stack = new Stack<int>();
 
        // Traverse the linked list and push values onto the
        // stack
        Node curr = head;
        while (curr != null) {
            stack.Push(curr.data);
            curr = curr.next;
        }
 
        int borrow = 1;
        Node new_head = null;
 
        // Pop elements from the stack and subtract borrow
        while (stack.Count > 0) {
            int val = stack.Pop() - borrow;
            borrow = 0;
            if (val < 0) {
                val += 10;
                borrow = 1;
            }
            Node new_node = NewNode(val);
            new_node.next = new_head;
            new_head = new_node;
        }
 
        // Remove leading zeros
        while (new_head != null && new_head.data == 0) {
            new_head = new_head.next;
        }
 
        return new_head;
    }
 
    // Function to print a linked list
    static void PrintList(Node node)
    {
        // Iterate until node is null
        while (node != null) {
            Console.Write(node.data);
            node = node.next;
        }
        Console.WriteLine();
    }
 
    // Driver code
    static void Main()
    {
        Node head = NewNode(1);
        head.next = NewNode(0);
        head.next.next = NewNode(0);
        head.next.next.next = NewNode(0);
 
        Console.Write("List is ");
        PrintList(head);
 
        head = SubtractOne(head);
 
        Console.Write("Resultant list is ");
        PrintList(head);
    }
}


Javascript




// Linked list Node
class Node {
    constructor(data) {
        this.data = data;
        this.next = null;
    }
}
 
// Function to create a new node with the given data
function new_node(data) {
    // Create a new node
    const new_node = new Node(data);
 
    // Return the created node
    return new_node;
}
 
// Function to subtract 1 from the given Linked List representation of number using stack
function subtract_one(head) {
    const stack = [];
 
    // Traverse the linked list and push values onto the stack
    let curr = head;
    while (curr !== null) {
        stack.push(curr.data);
        curr = curr.next;
    }
 
    let borrow = 1;
    let new_head = null;
 
    // Pop elements from the stack and subtract borrow
    while (stack.length > 0) {
        let val = stack.pop() - borrow;
        borrow = 0;
        if (val < 0) {
            val += 10;
            borrow = 1;
        }
        const new_node = new Node(val);
        new_node.next = new_head;
        new_head = new_node;
    }
 
    // Remove leading zeros
    while (new_head !== null && new_head.data === 0) {
        const temp = new_head;
        new_head = new_head.next;
        // Delete temp (Not required in JavaScript as memory management is automatic)
    }
 
    return new_head;
}
 
// Function to print a linked list
function print_list(node) {
    // Iterate until node is null
    while (node !== null) {
        console.log(node.data);
        node = node.next;
    }
}
 
// Driver Code
const head = new_node(1);
head.next = new_node(0);
head.next.next = new_node(0);
head.next.next.next = new_node(0);
 
console.log("List is:");
print_list(head);
 
const newHead = subtract_one(head);
 
console.log("Resultant list is:");
print_list(newHead);


Output

List is 1000
Resultant list is 999






Time Complexity: O(n)
Space Complexity: O(n)



Last Updated : 04 Oct, 2023
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