Add_1_to_a_Linked_List_Number.cpp

/*
struct Node
{
    int data;
    struct Node* next;

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

class Solution {
  public:
    int helper(Node* temp){
        if(temp == NULL) return 1;
        int carry = helper(temp->next);
        temp->data += carry;
        if(temp->data<10) return 0;
        temp->data=0;
        return 1;
    }
    Node* addOne(Node* head) {
        int carry = helper(head);
        if(carry == 1){
            Node* newNode  = new Node(1);
            newNode->next = head;
            head = newNode;
        }
        return head;
    }
};