Add_Number_Linked_Lists.cpp

/* node for linked list:

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

*/

class Solution {
  public:
    Node* reverseLL(Node* head){
        if(head==NULL)  return NULL;
        Node* curr=head,*prev=NULL,*next=NULL;
        while(curr!=NULL){
            next=curr->next;
            curr->next=prev;
            prev=curr;
            curr=next;
        }
        return prev;
    }
    Node* addTwoLists(Node* l1, Node* l2){
        l1=reverseLL(l1);
        l2=reverseLL(l2);
        Node* temp1=l1,*temp2=l2;
        Node* dummyNode=new Node(-1);
        dummyNode->next=NULL;
        Node* temp=dummyNode;
        int carry=0,sum=0;
        while(l1!=NULL || l2!=NULL || carry>0){
            sum=carry;
            if(l1!=NULL){
                sum+=l1->data;
                l1=l1->next;
            }
            if(l2!=NULL){
                sum+=l2->data;
                l2=l2->next;
            }
            temp->next=new Node(sum%10);
            temp=temp->next;
            carry=sum/10;
        }
        dummyNode=dummyNode->next;
        Node* final=reverseLL(dummyNode);
        while(final && final->data==0)
            final=final->next;
        return final;
    }
};