2. Add Two Numbers

You are given two non-empty linked lists representing two non-negative integers. 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.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

/** * 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) {        ListNode* head = new ListNode(0);        ListNode* sum = head;        int carry = 0, add = 0;        while(l1 != NULL && l2 != NULL){            int s = (l1->val + l2->val + carry);            add = s % 10;            carry = s / 10;            ListNode* tmp = new ListNode(add);            head->next = tmp;            head = tmp;            l1 = l1->next;            l2 = l2->next;        }        while(l1 != NULL){            int s = l1->val + carry;            add = s % 10;            carry = s / 10;            ListNode* tmp = new ListNode(add);            head->next = tmp;            head = tmp;            l1 = l1->next;        }        while(l2 != NULL){            int s = l2->val + carry;            add = s % 10;            carry = s / 10;            ListNode* tmp = new ListNode(add);            head->next = tmp;            head = tmp;            l2 = l2->next;        }        if(carry == 1){            ListNode* tmp = new ListNode(1);            head->next = tmp;        }        return sum->next;    }};