Sum of Linked Lists

• Time : O(n + m)
• Space : O(n + m)

c++

using namespace std;

// This is an input struct. Do not edit.
class LinkedList {
public:
  int value;
  LinkedList *next = nullptr;

  LinkedList(int value) { this->value = value; }
};

LinkedList *sumOfLinkedLists(LinkedList *linkedListOne,
                             LinkedList *linkedListTwo) {
    int append = 0;
    LinkedList* dummy = new LinkedList(-1);
    LinkedList* tail = dummy;
    while(linkedListOne and linkedListTwo) {
        int sum = append + linkedListOne->value + linkedListTwo->value;
        linkedListOne = linkedListOne->next;
        linkedListTwo = linkedListTwo->next;
        append = sum / 10;
        sum = sum % 10;
        LinkedList* newTail = new LinkedList(sum);
        tail->next = newTail;
        tail = newTail;
    }
    while(linkedListOne) {
        int sum = append + linkedListOne->value;
        linkedListOne = linkedListOne->next;
        append = sum / 10;
        sum = sum % 10;
        LinkedList* newTail = new LinkedList(sum);
        tail->next = newTail;
        tail = newTail;
    }
    while(linkedListTwo) {
        int sum = append + linkedListTwo->value;
        linkedListTwo = linkedListTwo->next;
        append = sum / 10;
        sum = sum % 10;
        LinkedList* newTail = new LinkedList(sum);
        tail->next = newTail;
        tail = newTail;
    }
    if(append) {
        LinkedList* newTail = new LinkedList(append);
        tail->next = newTail;
        tail = newTail;
    }
    return dummy->next;
}