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; } * } */public class Solution {    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {    if(l1==null) return l2;    if(l2==null) return l1;    ListNode head = new ListNode(0);    ListNode cur = head;    int flag = 0;    while(l1!=null&&l2!=null){    int t = (l1.val+l2.val+flag);    cur.next = new ListNode(t%10);    flag = t/10;    cur = cur.next;    l1 = l1.next;    l2 = l2.next;    }    while(l1!=null){    int t = (l1.val+flag);    cur.next = new ListNode(t%10);    flag = t/10;    cur = cur.next;    l1 = l1.next;    }    while(l2!=null){    int t = (l2.val+flag);    cur.next = new ListNode(t%10);    flag = t/10;    cur = cur.next;    l2 = l2.next;    }        if(flag>0){    cur.next = new ListNode(flag);    }    return head.next;    }}