You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list. Input: (2 -> 4 -> 3) + (5 -> 6 -> 4) Output: 7 -> 0 -> 8

Add Two Numbers.cpp

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int left = 0;
        ListNode root(-1);
        ListNode* cur = &root;
        
        while(l1 != NULL or l2 != NULL or left != 0) {
            int sum = 0;
            sum += (l1 == NULL ? 0 : l1->val);
            sum += (l2 == NULL ? 0 : l2->val);
            sum += left;
            
            left = 0;
            if(sum > 9) {
                sum -= 10;
                ++left;
            }
            
            cur->next = new ListNode(sum);
            cur = cur->next;
            if(l1 != NULL) {
                l1 = l1->next;
            }
            if(l2 != NULL) {
                l2 = l2->next;
            }
            
            
            
        }
        
        return root.next;
        
    }
};