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：
注意以下两点，其它都简单：
- 两个链表长度不一样。
- 进位的处理。
1 class Solution { 2 public: 3 void insertNode(ListNode *node, ListNode *&head, ListNode *&tail) { 4 if (NULL == head) { 5 head = tail = node; 6 } 7 else { 8 tail->next = node; 9 tail = node;10 }11 }12 13 ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {14 ListNode *head = NULL, *tail = NULL;15 int sum, flag = 0;16 17 while ((l1 != NULL) || (l2 != NULL)) {18 sum = ((l1 != NULL) ? l1->val : 0) + ((l2 != NULL) ? l2->val : 0) + flag;19 flag = sum / 10;20 insertNode(new ListNode(sum % 10), head, tail);21 22 l1 = (l1 != NULL) ? l1->next : NULL;23 l2 = (l2 != NULL) ? l2->next : NULL;24 }25 26 if (flag > 0) {27 insertNode(new ListNode(flag), head, tail);28 }29 30 return head;31 }32 };