Add Two Numbers

/**
 * 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 p1 = l1;
        ListNode p2 = l2;
        ListNode h = new ListNode(0);//创建一个头结点
        ListNode r = h;//设立一个尾指针
        int carry = 0;//进位
        int sum = 0;//对应位及进位相加之和
        while(p1!=null||p2!=null) {
            
            if(p1!=null&&p2!=null){
                sum = p1.val+p2.val+carry;
                p1 = p1.next;
                p2 = p2.next;
            }
            
            else {
                if(p1==null) {
                    sum = p2.val+carry;
                    p2 = p2.next;
                }
                else {
                    sum = p1.val+carry;
                    p1 = p1.next;
                }
            }
            
            if(sum>=10) {
                sum = sum-10;
                carry = 1;
            }
            else {
                carry = 0;
            }
            ListNode p = new ListNode(sum);
            r.next = p;
            r = p;
        }
        if(carry==1) {
            ListNode p = new ListNode(1);
            r.next = p;
            r = p;
        }
        return h.next;
    }
}