Unflatten List

void unflattenList(Node *head, Node **tail){
    recursiveUnflatten(head);

    Node *cur=head;

    while(cur->next)
        cur=cur->next;

    *tail=cur;
}

void recursiveUnflatten(Node *child){
    Node *cur=child;

    while(cur){
        if(cur->child){
            //break link
            ((cur->child)->prev)->next=NULL;
            (cur->child)->prev=NULL;
            //recursion
            recursiveUnflatten(cur->child);
        }
        cur=cur->next;
    }
}