Add Two Numbers

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.

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

class Solution {    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {    ListNode res=new ListNode(0);    ListNode cop=res;    int sum=0;    while(l1!=null||l2!=null){       int x=(l1!=null)?l1.val:0;       int y=(l2!=null)?l2.val:0;        sum=x+y+sum;          cop.next=new ListNode(sum%10);        sum/=10;              if(l1!=null) l1=l1.next;        if(l2!=null) l2=l2.next;                cop=cop.next;    }    if(sum>0){        cop.next=new ListNode(sum);    }    return res.next;}}