2.Add Two Numbers-两个单链表相加

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) {
        ListNode c1 = l1;//定义两个指针变量 c1 c2
        ListNode c2 = l2;
        ListNode head = new ListNode(0);//定义一个新链表的头结点
        ListNode d = head;//新链表的指针变量
        int sum = 0;
        while(c1 != null || c2 != null) {
            if(c1 != null) {
                sum = sum + c1.val;
                c1 = c1.next;
            }
            if(c2 != null) {
                sum = sum + c2.val;
                c2 = c2.next;
            }
            d.next = new ListNode(sum%10);
            d = d.next;
            sum = sum /10;
        }
        if(sum == 1) {
            d.next = new ListNode(1);
        }
        return head.next;
        
        
    }
}