PROGRAM:

class Solution
{
public:
//Function to add two numbers represented by linked list.
Node*reverse(struct Node*head){
Node*curr=head;
Node*prev=NULL;
Node*nxt;
while(curr!=NULL){
nxt=curr->next;
curr->next=prev;
prev=curr;
curr=nxt;
}
return prev;
}
public:
struct Node* addTwoLists(struct Node* first, struct Node* second)
...

PROGRAM:

Node*merge(Node*a,Node*b){//a=root b=root ka right wala
if(a==NULL)return b;
if(b==NULL)return a;
Node*res;
if(a->datadata)
{
res=a;
res->bottom=merge(a->bottom,b);
}
else{
res=b;
res->bottom=merge(a,b->bottom);
}
res->next=NULL;
return res;
}
Node *flatten(Node *root)
{
if(root==NULL || root->next==NULL)...