LeetCode - Add Two Numbers

Question

Link:https://leetcode.com/problems/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

Code

一个一般的版本。（C++ : 40ms）

/**
* 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 *head = new ListNode(-1);
ListNode *tail = head;
int carry = 0;
while(l1 != NULL || l2 != NULL){
if(l1 != NULL && l2 != NULL){
int sum = l1->val + l2->val + carry;
ListNode *node = new ListNode(sum % 10);
carry = sum / 10;
tail->next = node;
tail = tail->next;
l1 = l1->next;
l2 = l2->next;
}
else if(l1 != NULL){
tail->next = l1;
ListNode *temp = l1;
while(temp != NULL){
if(carry == 1){
int sum = temp->val + carry;
temp->val = sum % 10;
carry = sum / 10;
}
tail = temp;
temp = temp->next;
}
l1 = temp;
}
else if(l2 != NULL){
tail->next = l2;
ListNode *temp = l2;
while(temp != NULL){
if(carry == 1){
int sum = temp->val + carry;
temp->val = sum % 10;
carry = sum / 10;
}
tail = temp;
temp = temp->next;
}
l2 = temp;
}
}

if(carry == 1){
ListNode *node = new ListNode(1);
tail->next = node;
}

return head->next;
}
};