Add_1_to_a_SLL.cpp

//{ Driver Code Starts
// Initial template for C++

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

struct Node {
    int data;
    struct Node* next;

    Node(int x) {
        data = x;
        next = NULL;
    }
};

void printList(Node* node) {
    while (node != NULL) {
        cout << node->data % 10;
        node = node->next;
    }
    cout << "\n";
}


// } Driver Code Ends
// User function template for C++

/*

struct Node
{
    int data;
    struct Node* next;

    Node(int x){
        data = x;
        next = NULL;
    }
};

*/

class Solution {  
public:  
    Node* reverse(Node* head) {  
        Node* temp = head;  
        Node* front = NULL;  
        Node* prev = NULL;  
        
        while (temp != NULL) 
        {  
            front = temp->next;   
            temp->next = prev;    
            prev = temp;         
            temp = front;      
        }  
        return prev; 
    }  
    
    Node* addOne(Node* head) {  
        head = reverse(head); 
        Node * temp = head;
        int carry = 1;                
        
        while (temp != NULL) 
        {  
            temp->data += carry;   
            if (temp->data < 10) 
            {  
                carry = 0;   
                break;   
            } 
            else 
            {  
                temp->data = 0;   
                carry = 1;  
            }  
            temp = temp->next; 
        }  

        if (carry == 1)
        {  
            Node* newnode = new Node(1);  
            head = reverse(head); 
            newnode->next = head;   
            return newnode; 
        }  
        
        head = reverse(head);   
        return head;
    }  
};


//{ Driver Code Starts.

int main() {
    int t;
    cin >> t;
    cin.ignore();
    while (t--) {
        vector<int> arr;
        string input;
        getline(cin, input);
        stringstream ss(input);
        int number;
        while (ss >> number) {
            arr.push_back(number);
        }

        if (arr.empty()) {
            cout << -1 << endl;
            continue;
        }

        int data = arr[0];
        struct Node* head = new Node(data);
        struct Node* tail = head;
        for (int i = 1; i < arr.size(); ++i) {
            data = arr[i];
            tail->next = new Node(data);
            tail = tail->next;
        }
        Solution ob;
        head = ob.addOne(head);
        printList(head);
    }
    return 0;
}

// } Driver Code Ends