leetcode Add Two Numbers

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

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode temp1,temp2;
        temp1=l1;
        temp2=l2;
        int flag=0;
        int sum=0,v1=0,v2=0;
        ListNode res=new ListNode(-1);
        ListNode curr=res;
        while (temp1!=null || temp2!=null) {
            if (temp1==null) {
                v1=0;
            }else {
                v1=temp1.val;
            }
            if (temp2==null) {
                v2=0;
            }else {
                v2=temp2.val;
            }
            sum=v1+v2+flag;
            if (sum>=10) {
                sum=sum-10;
                flag=1;
            }else {
                flag=0;
            }
            ListNode node=new ListNode(sum);
            curr.next=node;
            curr=curr.next;
            if (temp1!=null) {
                temp1=temp1.next;
            }
            if (temp2!=null) {
                temp2=temp2.next;
            }
        }
        if (flag>0) {
            curr.next=new ListNode(1);
        }
        return res.next;
    }
}