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

思路非常简单，利用两个指针分别遍历两个链表，并且用一个变量表示是否有进位。某个链表遍历结束之后再将另一个链表连接在结果链表之后即可，若最后有进位需要添加一位。

/**  * 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 carry = 0;          ListNode* tail = new ListNode(0);          ListNode* ptr = tail;                    while(l1 != NULL || l2 != NULL){              int val1 = 0;              if(l1 != NULL){                  val1 = l1->val;                  l1 = l1->next;              }                            int val2 = 0;              if(l2 != NULL){                  val2 = l2->val;                  l2 = l2->next;              }                            int tmp = val1 + val2 + carry;              ptr->next = new ListNode(tmp % 10);              carry = tmp / 10;              ptr = ptr->next;          }                    if(carry == 1){              ptr->next = new ListNode(1);          }          return tail->next;      }  };