2.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode();
        ListNode cur = dummy;
        int carry = 0;
        while(l1!=null||l2!=null||carry!=0){
            if(l1!=null){
                carry+=l1.val;
            }
            if(l2!=null){
                carry+=l2.val;
            }
            cur = cur.next = new ListNode(carry%10);
            carry /= 10;
            if(l1!=null){
                l1 = l1.next;
            }
            if(l2!=null){
                l2 = l2.next;
            }
        }
        return dummy.next;
    }
}