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

1 public class Solution { 2     public ListNode addTwoNumbers(ListNode l1, ListNode l2) { 3         ListNode head = new ListNode(-1); 4         ListNode pre = head; 5         ListNode p1 = l1; 6         ListNode p2=l2; 7         int carry = 0; 8         while(p1!=null&&p2!=null){ 9             int sum = p1.val+p2.val+carry;10             carry = sum/10;11             sum = sum%10;12             pre.next = new ListNode(sum);13             pre =pre.next; 14             p1 = p1.next; 15             p2=p2.next;16         }17         while(p1!=null){18             int sum = p1.val+carry;19             carry = sum/10;20             sum = sum%10;21             pre.next = new ListNode(sum);22             p1= p1.next;23             pre = pre.next;24         }25         while(p2!=null){26             int sum = p2.val+carry;27             carry = sum/10;28             sum = sum%10;29             pre.next = new ListNode(sum);30             p2 = p2.next;31             pre = pre.next;32         }33         if(carry>0){34             pre.next = new ListNode(carry);35         }36         return head.next;37     }38 }