Add 1 to a number represented as linked list

Number is represented in linked list such that each digit corresponds to a node in linked list. Add 1 to it. For example 1999 is represented as (1-> 9-> 9 -> 9) and adding 1 to it should change it to (2->0->0->0) 

Below are the steps : 

  1. Reverse given linked list. For example, 1-> 9-> 9 -> 9 is converted to 9-> 9 -> 9 ->1.
  2. Start traversing linked list from leftmost node and add 1 to it. If there is a carry, move to the next node. Keep moving to the next node while there is a carry.
  3. Reverse modified linked list and return head.

Below is the implementation of above steps. 

C++

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// C++ program to add 1 to a linked list
#include <bits/stdc++.h>
using namespace std;
 
/* Linked list node */
class Node
{
    public:
    int data;
    Node* next;
};
 
/* Function to create a new node with given data */
Node *newNode(int data)
{
    Node *new_node = new Node;
    new_node->data = data;
    new_node->next = NULL;
    return new_node;
}
 
/* Function to reverse the linked list */
Node *reverse(Node *head)
{
    Node * prev = NULL;
    Node * current = head;
    Node * next;
    while (current != NULL)
    {
        next = current->next;
        current->next = prev;
        prev = current;
        current = next;
    }
    return prev;
}
 
/* Adds one to a linked lists and return the head
node of resultant list */
Node *addOneUtil(Node *head)
{
    // res is head node of the resultant list
    Node* res = head;
    Node *temp, *prev = NULL;
 
    int carry = 1, sum;
 
    while (head != NULL) //while both lists exist
    {
        // Calculate value of next digit in resultant list.
        // The next digit is sum of following things
        // (i) Carry
        // (ii) Next digit of head list (if there is a
        // next digit)
        sum = carry + head->data;
 
        // update carry for next calulation
        carry = (sum >= 10)? 1 : 0;
 
        // update sum if it is greater than 10
        sum = sum % 10;
 
        // Create a new node with sum as data
        head->data = sum;
 
        // Move head and second pointers to next nodes
        temp = head;
        head = head->next;
    }
 
    // if some carry is still there, add a new node to
    // result list.
    if (carry > 0)
        temp->next = newNode(carry);
 
    // return head of the resultant list
    return res;
}
 
// This function mainly uses addOneUtil().
Node* addOne(Node *head)
{
    // Reverse linked list
    head = reverse(head);
 
    // Add one from left to right of reversed
    // list
    head = addOneUtil(head);
 
    // Reverse the modified list
    return reverse(head);
}
 
// A utility function to print a linked list
void printList(Node *node)
{
    while (node != NULL)
    {
        cout << node->data;
        node = node->next;
    }
    cout<<endl;
}
 
/* Driver program to test above function */
int main(void)
{
    Node *head = newNode(1);
    head->next = newNode(9);
    head->next->next = newNode(9);
    head->next->next->next = newNode(9);
 
    cout << "List is ";
    printList(head);
 
    head = addOne(head);
 
    cout << "\nResultant list is ";
    printList(head);
 
    return 0;
}
 
// This is code is contributed by rathbhupendra

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C


// C program to add 1 to a linked list
#include<bits/stdc++.h>

/* Linked list node */
struct Node
{
    int data;
    Node* next;
};

/* Function to create a new node with given data */
Node *newNode(int data)
{
    Node *new_node = new Node;
    new_node->data = data;
    new_node->next = NULL;
    return new_node;
}

/* Function to reverse the linked list */
Node *reverse(Node *head)
{
    Node * prev   = NULL;
    Node * current = head;
    Node * next;
    while (current != NULL)
    {
        next  = current->next;
        current->next = prev;
        prev = current;
        current = next;
    }
    return prev;
}

/* Adds one to a linked lists and return the head
   node of resultant list */
Node *addOneUtil(Node *head)
{
    // res is head node of the resultant list
    Node* res = head;
    Node *temp, *prev = NULL;

    int carry = 1, sum;

    while (head != NULL) //while both lists exist
    {
        // Calculate value of next digit in resultant list.
        // The next digit is sum of following things
        // (i) Carry
        // (ii) Next digit of head list (if there is a
        //     next digit)
        sum = carry + head->data;

        // update carry for next calulation
        carry = (sum >= 10)? 1 : 0;

        // update sum if it is greater than 10
        sum = sum % 10;

        // Create a new node with sum as data
        head->data = sum;

        // Move head and second pointers to next nodes
        temp = head;
        head = head->next;
    }

    // if some carry is still there, add a new node to
    // result list.
    if (carry > 0)
        temp->next = newNode(carry);

    // return head of the resultant list
    return res;
}

// This function mainly uses addOneUtil().
Node* addOne(Node *head)
{
    // Reverse linked list
    head = reverse(head);

    // Add one from left to right of reversed
    // list
    head = addOneUtil(head);

    // Reverse the modified list
    return reverse(head);
}

// A utility function to print a linked list
void printList(Node *node)
{
    while (node != NULL)
    {
        printf("%d", node->data);
        node = node->next;
    }
    printf("\n");
}

/* Driver program to test above function */
int main(void)
{
    Node *head = newNode(1);
    head->next = newNode(9);
    head->next->next = newNode(9);
    head->next->next->next = newNode(9);

    printf("List is ");
    printList(head);

    head = addOne(head);

    printf("\nResultant list is ");
    printList(head);

    return 0;
}

Java

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// Java program to add 1 to a linked list
class GfG {
 
    /* Linked list node */
    static class Node {
        int data;
        Node next;
    }
 
    /* Function to create a new node with given data */
    static Node newNode(int data)
    {
        Node new_node = new Node();
        new_node.data = data;
        new_node.next = null;
        return new_node;
    }
 
    /* Function to reverse the linked list */
    static Node reverse(Node head)
    {
        Node prev = null;
        Node current = head;
        Node next = null;
        while (current != null) {
            next = current.next;
            current.next = prev;
            prev = current;
            current = next;
        }
        return prev;
    }
 
    /* Adds one to a linked lists and return the head
    node of resultant list */
    static Node addOneUtil(Node head)
    {
        // res is head node of the resultant list
        Node res = head;
        Node temp = null, prev = null;
 
        int carry = 1, sum;
 
        while (head != null) // while both lists exist
        {
            // Calculate value of next digit in resultant
            // list. The next digit is sum of following
            // things (i) Carry (ii) Next digit of head list
            // (if there is a next digit)
            sum = carry + head.data;
 
            // update carry for next calulation
            carry = (sum >= 10) ? 1 : 0;
 
            // update sum if it is greater than 10
            sum = sum % 10;
 
            // Create a new node with sum as data
            head.data = sum;
 
            // Move head and second pointers to next nodes
            temp = head;
            head = head.next;
        }
 
        // if some carry is still there, add a new node to
        // result list.
        if (carry > 0)
            temp.next = newNode(carry);
 
        // return head of the resultant list
        return res;
    }
 
    // This function mainly uses addOneUtil().
    static Node addOne(Node head)
    {
        // Reverse linked list
        head = reverse(head);
 
        // Add one from left to right of reversed
        // list
        head = addOneUtil(head);
 
        // Reverse the modified list
        return reverse(head);
    }
 
    // A utility function to print a linked list
    static void printList(Node node)
    {
        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(9);
        head.next.next = newNode(9);
        head.next.next.next = newNode(9);
 
        System.out.print("List is ");
        printList(head);
 
        head = addOne(head);
        System.out.println();
        System.out.print("Resultant list is ");
        printList(head);
    }
}
 
// This code is contributed by prerna saini

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Python3

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# Python3 program to add 1 to a linked list
import sys
import math
 
# Linked list node
 
 
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None
 
# Function to create a new node with given data */
 
 
def newNode(data):
    return Node(data)
 
# Function to reverse the linked list */
 
 
def reverseList(head):
    if not head:
        return
    curNode = head
    prevNode = head
    nextNode = head.next
    curNode.next = None
 
    while(nextNode):
        curNode = nextNode
        nextNode = nextNode.next
        curNode.next = prevNode
        prevNode = curNode
 
    return curNode
 
# Adds one to a linked lists and return the head
# node of resultant list
 
 
def addOne(head):
 
    # Reverse linked list and add one to head
    head = reverseList(head)
    k = head
    carry = 0
    prev = None
    head.data += 1
 
    # update carry for next calulation
    while(head != None) and (head.data > 9 or carry > 0):
        prev = head
        head.data += carry
        carry = head.data // 10
        head.data = head.data % 10
        head = head.next
 
    if carry > 0:
        prev.next = Node(carry)
    # Reverse the modified list
    return reverseList(k)
 
# A utility function to print a linked list
 
 
def printList(head):
    if not head:
        return
    while(head):
        print("{}".format(head.data), end="")
        head = head.next
 
 
# Driver code
if __name__ == '__main__':
    head = newNode(1)
    head.next = newNode(9)
    head.next.next = newNode(9)
    head.next.next.next = newNode(9)
 
    print("List is: ", end="")
    printList(head)
 
    head = addOne(head)
 
    print("\nResultant list is: ", end="")
    printList(head)
 
 
# This code is contributed by Rohit

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C#

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// C# program to add 1 to a linked list
using System;
 
class GfG {
 
    /* Linked list node */
    public class Node {
        public int data;
        public Node next;
    }
 
    /* Function to create a new node with given data */
    static Node newNode(int data)
    {
        Node new_node = new Node();
        new_node.data = data;
        new_node.next = null;
        return new_node;
    }
 
    /* Function to reverse the linked list */
    static Node reverse(Node head)
    {
        Node prev = null;
        Node current = head;
        Node next = null;
        while (current != null) {
            next = current.next;
            current.next = prev;
            prev = current;
            current = next;
        }
        return prev;
    }
 
    /* Adds one to a linked lists and return the head
    node of resultant list */
    static Node addOneUtil(Node head)
    {
        // res is head node of the resultant list
        Node res = head;
        Node temp = null, prev = null;
 
        int carry = 1, sum;
 
        while (head != null) // while both lists exist
        {
            // Calculate value of next digit in resultant
            // list. The next digit is sum of following
            // things (i) Carry (ii) Next digit of head list
            // (if there is a next digit)
            sum = carry + head.data;
 
            // update carry for next calulation
            carry = (sum >= 10) ? 1 : 0;
 
            // update sum if it is greater than 10
            sum = sum % 10;
 
            // Create a new node with sum as data
            head.data = sum;
 
            // Move head and second pointers to next nodes
            temp = head;
            head = head.next;
        }
 
        // if some carry is still there, add a new node to
        // result list.
        if (carry > 0)
            temp.next = newNode(carry);
 
        // return head of the resultant list
        return res;
    }
 
    // This function mainly uses addOneUtil().
    static Node addOne(Node head)
    {
        // Reverse linked list
        head = reverse(head);
 
        // Add one from left to right of reversed
        // list
        head = addOneUtil(head);
 
        // Reverse the modified list
        return reverse(head);
    }
 
    // A utility function to print a linked list
    static void printList(Node node)
    {
        while (node != null) {
            Console.Write(node.data);
            node = node.next;
        }
        Console.WriteLine();
    }
 
    /* Driver code */
    public static void Main(String[] args)
    {
        Node head = newNode(1);
        head.next = newNode(9);
        head.next.next = newNode(9);
        head.next.next.next = newNode(9);
 
        Console.Write("List is ");
        printList(head);
 
        head = addOne(head);
        Console.WriteLine();
        Console.Write("Resultant list is ");
        printList(head);
    }
}
 
// This code contributed by Rajput-Ji

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Output



List is 1999

Resultant list is 2000

  
Recursive Implementation: 
We can recursively reach the last node and forward carry to previous nodes. Recursive solution doesn’t require reversing of linked list. We can also use a stack in place of recursion to temporarily hold nodes.

Below is the implementation of recursive solution.

C++

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// Recursive C++ program to add 1 to a linked list
#include <bits/stdc++.h>
 
/* Linked list node */
struct Node {
    int data;
    Node* next;
};
 
/* Function to create a new node with given data */
Node* newNode(int data)
{
    Node* new_node = new Node;
    new_node->data = data;
    new_node->next = NULL;
    return new_node;
}
 
// Recursively add 1 from end to beginning and returns
// carry after all nodes are processed.
int addWithCarry(Node* head)
{
    // If linked list is empty, then
    // return carry
    if (head == NULL)
        return 1;
 
    // Add carry returned be next node call
    int res = head->data + addWithCarry(head->next);
 
    // Update data and return new carry
    head->data = (res) % 10;
    return (res) / 10;
}
 
// This function mainly uses addWithCarry().
Node* addOne(Node* head)
{
    // Add 1 to linked list from end to beginning
    int carry = addWithCarry(head);
 
    // If there is carry after processing all nodes,
    // then we need to add a new node to linked list
    if (carry) {
        Node* newNode = new Node;
        newNode->data = carry;
        newNode->next = head;
        return newNode; // New node becomes head now
    }
 
    return head;
}
 
// A utility function to print a linked list
void printList(Node* node)
{
    while (node != NULL) {
        printf("%d", node->data);
        node = node->next;
    }
    printf("\n");
}
 
/* Driver code */
int main(void)
{
    Node* head = newNode(1);
    head->next = newNode(9);
    head->next->next = newNode(9);
    head->next->next->next = newNode(9);
 
    printf("List is ");
    printList(head);
 
    head = addOne(head);
 
    printf("\nResultant list is ");
    printList(head);
 
    return 0;
}

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Java

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// Recursive Java program to add 1 to a linked list
class GfG {
 
    /* Linked list node */
    static class Node
    {
        int data;
        Node next;
    }
 
    /* Function to create a new node with given data */
    static Node newNode(int data)
    {
        Node new_node = new Node();
        new_node.data = data;
        new_node.next = null;
        return new_node;
    }
 
    // Recursively add 1 from end to beginning and returns
    // carry after all nodes are processed.
    static int addWithCarry(Node head)
    {
 
        // If linked list is empty, then
        // return carry
        if (head == null)
            return 1;
 
        // Add carry returned be next node call
        int res = head.data + addWithCarry(head.next);
 
        // Update data and return new carry
        head.data = (res) % 10;
        return (res) / 10;
    }
 
    // This function mainly uses addWithCarry().
    static Node addOne(Node head)
    {
 
        // Add 1 to linked list from end to beginning
        int carry = addWithCarry(head);
 
        // If there is carry after processing all nodes,
        // then we need to add a new node to linked list
        if (carry > 0)
        {
            Node newNode = newNode(carry);
            newNode.next = head;
            return newNode; // New node becomes head now
        }
 
        return head;
    }
 
    // A utility function to print a linked list
    static void printList(Node node)
    {
        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(9);
        head.next.next = newNode(9);
        head.next.next.next = newNode(9);
 
        System.out.print("List is ");
        printList(head);
 
        head = addOne(head);
        System.out.println();
        System.out.print("Resultant list is ");
        printList(head);
    }
}
 
// This code is contributed by shubham96301

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Python

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# Recursive Python program to add 1 to a linked list
 
# Node class
class Node:
 
    # Constructor to initialize the node object
    def __init__(self, data):
        self.data = data
        self.next = None
 
# Function to create a new node with given data
def newNode(data):
 
    new_node = Node(0)
    new_node.data = data
    new_node.next = None
    return new_node
 
# Recursively add 1 from end to beginning and returns
# carry after all nodes are processed.
def addWithCarry(head):
 
    # If linked list is empty, then
    # return carry
    if (head == None):
        return 1
 
    # Add carry returned be next node call
    res = head.data + addWithCarry(head.next)
 
    # Update data and return new carry
    head.data = int((res) % 10)
    return int((res) / 10)
 
# This function mainly uses addWithCarry().
def addOne(head):
 
    # Add 1 to linked list from end to beginning
    carry = addWithCarry(head)
 
    # If there is carry after processing all nodes,
    # then we need to add a new node to linked list
    if (carry != 0):
     
        newNode = Node(0)
        newNode.data = carry
        newNode.next = head
        return newNode # New node becomes head now
     
    return head
 
# A utility function to print a linked list
def printList(node):
 
    while (node != None):
     
        print( node.data,end = "")
        node = node.next
     
    print("\n")
 
# Driver program to test above function
 
head = newNode(1)
head.next = newNode(9)
head.next.next = newNode(9)
head.next.next.next = newNode(9)
 
print("List is ")
printList(head)
 
head = addOne(head)
 
print("\nResultant list is ")
printList(head)
 
 
# This code is contributed by Arnab Kundu

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C#

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// Recursive C# program to add 1 to a linked list
using System;
 
class GfG
{
 
    /* Linked list node */
    public class Node
    {
        public int data;
        public Node next;
    }
 
    /* Function to create a new node with given data */
    public static Node newNode(int data)
    {
        Node new_node = new Node();
        new_node.data = data;
        new_node.next = null;
        return new_node;
    }
 
    // Recursively add 1 from end to beginning and returns
    // carry after all nodes are processed.
    public static int addWithCarry(Node head)
    {
 
        // If linked list is empty, then
        // return carry
        if (head == null)
            return 1;
 
        // Add carry returned be next node call
        int res = head.data + addWithCarry(head.next);
 
        // Update data and return new carry
        head.data = (res) % 10;
        return (res) / 10;
    }
 
    // This function mainly uses addWithCarry().
    public static Node addOne(Node head)
    {
 
        // Add 1 to linked list from end to beginning
        int carry = addWithCarry(head);
        Node newNodes = null;
         
        // If there is carry after processing all nodes,
        // then we need to add a new node to linked list
        if (carry > 0)
        {
            newNodes = newNode(carry);
            newNodes.next = head;
            return newNodes; // New node becomes head now
        }
 
        return head;
    }
 
    // A utility function to print a linked list
    public static void printList(Node node)
    {
        while (node != null)
        {
            Console.Write(node.data);
            node = node.next;
        }
        Console.WriteLine();
    }
 
    /* Driver code */
    public static void Main(String[] args)
    {
        Node head = newNode(1);
        head.next = newNode(9);
        head.next.next = newNode(9);
        head.next.next.next = newNode(9);
 
        Console.Write("List is ");
        printList(head);
 
        head = addOne(head);
        Console.WriteLine();
        Console.Write("Resultant list is ");
        printList(head);
    }
}
 
/* This code contributed by PrinciRaj1992 */

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Output

List is 1999

Resultant list is 2000

https://www.youtube.com/watch?v=utc8bwTDjLk
This article is contributed by Aditya Goel. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above
 

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