## 刷题内容

You are given two non-empty linked lists representing two non-negative integers. 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.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.


## 解题方案

class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
if (l1 == null) {
return l2;
}
if (l2 == null) {
return l1;
}

int tmp = 0;
while(l1 != null || l2 != null || tmp != 0) {
if(l1 != null) {
tmp += l1.val;
l1 = l1.next;
}
if(l2 != null) {
tmp += l2.val;
l2 = l2.next;
}

p.next = new ListNode(tmp % 10);
p = p.next;
tmp = tmp / 10;
}
}
}


class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
if (l1 == null && l2 == null) {
return null;
} else if (l1 == null || l2 == null) {
return l1 != null ? l1: l2;
} else {
ListNode l3;
if (l1.val + l2.val < 10) {
l3 = new ListNode(l1.val + l2.val);