[LeetCode] Add Two Numbers

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

Solutions:

/**

 * 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 *ans = NULL, *end = NULL, *num1 = l1, *num2 = l2;

        int carry = 0, sum = 0;

        while(true)

        {

            if(num1 != NULL)

            {

                if(num2 != NULL)

                {

                    sum = num1 -> val + num2 -> val + carry;

                    carry = sum / 10;

                    if(ans == NULL)

                    {

                        ans = new ListNode(sum % 10);

                        end = ans;

                    }

                    else

                    {

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

                        end = end -> next;

                    }

                    num1 = num1 -> next;

                    num2 = num2 -> next;

                }

                else

                {

                    sum = num1 -> val + carry;

                    carry = sum / 10;

                    if(ans == NULL)

                    {

                        ans = new ListNode(sum % 10);

                        end = ans;

                    }

                    else

                    {

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

                        end = end -> next;

                    }

                    num1 = num1 -> next;

                }

            }

            else

            {

                if(num2 != NULL)

                {

                    sum = num2 -> val + carry;

                    carry = sum / 10;

                    if(ans == NULL)

                    {

                        ans = new ListNode(sum % 10);

                        end = ans;

                    }

                    else

                    {

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

                        end = end -> next;

                    }

                    num2 = num2 -> next;

                }

                else

                {

                    if(carry == 1)

                    {

                        end -> next = new ListNode(1);

                        end = end -> next;

                    }

                    break;

                }

            }

        }

        

        return ans;

    }

};