【leetcode】Add Two Numbers

Question：

 

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

 

Anwser 1：

 

/**

 * 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

        if(l1 == NULL && l2 == NULL) {

            return NULL;

        }

        

        ListNode *retList = new ListNode(0);

        ListNode *tmpList = retList;

        

        ListNode *head1 = l1;

        ListNode *head2 = l2;

        int carry = 0;

        while(head1 != NULL && head2 != NULL){

            int sum = carry + head1->val + head2->val;

            carry = sum / 10;

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

            tmpList = tmpList->next;

            

            head1 = head1->next;

            head2 = head2->next;

        }

        

        while(head1 != NULL){

            int sum = carry + head1->val;

            carry = sum / 10;

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

            tmpList = tmpList->next;

            

            head1 = head1->next;

        }

        

        while(head2 != NULL){

            int sum = carry + head2->val;

            carry = sum / 10;

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

            tmpList = tmpList->next;

            

            head2 = head2->next;

        }

        

        if(carry == 1){

            tmpList->next = new ListNode(1);

        }

        tmpList = retList;

        retList = retList->next;

        

        delete tmpList;

        

        return retList;

    }

};

 

Anwser 2：