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 = null, cur = null;
        //进位
        int carry = 0;
        while(l1 != null && l2 != null){
            ListNode newNode = new ListNode(l1.val+l2.val+carry);
            if(newNode.val > 9){
                carry = 1;
                newNode.val -= 10;
            }
            else{
                carry = 0;
            }
            if(head == null){
                head = newNode;
            }
            else{
                cur.next = newNode;
            }
            cur = newNode;
            l1 = l1.next;
            l2 = l2.next;
        }

        ListNode tail = cur;
        if(l1 == null){
            cur.next = l2;
            cur = l2;
        }
        else{
            cur.next = l1;
            cur = l1;
        }

        while(cur != null){
            if(carry+cur.val == 10){
                cur.val = 0;
                carry = 1;
            }
            else{
                cur.val += carry;
                carry = 0;
            }
            if(cur.next == null){
                tail = cur;
            }
            cur = cur.next;
        }
        if(carry == 1){
            tail.next = new ListNode(1);
        }

        return head;
    }
}