2. Add Two Numbers

问题描述：

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

下面附代码：

/**
* Definition for singly-linked list.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
int c = 0;
ListNode l3 = new ListNode(0);
ListNode current = l3;

while(l1!=null && l2!=null){
int sum = l1.val + l2.val + c;
current.next = new ListNode(sum % 10);
current = current.next;
c = sum / 10;
l1 = l1.next;
l2 = l2.next;
}

while(l1!=null){
int sum = l1.val+c;
current.next = new ListNode(sum % 10);
current = current.next;
c = sum / 10;
l1 = l1.next;
}

while(l2!=null){
int sum = l2.val+c;
current.next = new ListNode(sum % 10);
current = current.next;
c = sum / 10;
l2 = l2.next;
}

if(c==1){
current.next = new ListNode(1);
current = current.next;
}

current.next = null;
return l3.next;
}
}