2.Add Two Numbers (List)

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
 

/**

 * 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) {

        int sum = l1->val + l2->val; 

        int carry = sum/10;

        ListNode* root = new ListNode(sum%10);

        ListNode* current = root;

        

        l1 = l1->next;

        l2 = l2->next;

        while(l1 && l2){

            sum = l1->val + l2->val + carry;

            carry = sum/10;

            current->next = new ListNode(sum%10);

            current = current->next;

            l1 = l1->next;

            l2 = l2->next;

        }

        

        while(l1){

            sum = l1->val+ carry;

            carry = sum/10;

            current->next = new ListNode(sum%10);

            current = current->next; 

            l1 = l1->next;

        }

        

        while(l2){

            sum = l2->val+ carry;

            carry = sum/10;

            current->next = new ListNode(sum%10);

            current = current->next; 

            l2 = l2->next;

        }

        

        if(carry){

            current->next = new ListNode(carry);

        }

        return root;

    }

};