Leetcode题目分析 2. Add Two Numbers

/**
* 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 resultHead = new ListNode(0);
ListNode pointer = resultHead;
//表示上次相加是否产生进位。
int remain = 0;
while(true){
if(l1 == null && l2 == null){
break;
} else if(l1 == null && l2 != null){
if(l2.val + remain >= 10){
pointer.next = new ListNode(l2.val + remain - 10);
remain = 1;
} else{
pointer.next = new ListNode(l2.val + remain);
remain = 0;
}
l2 = l2.next;
pointer = pointer.next;

} else if(l1 != null && l2 == null){
if(l1.val + remain >= 10){
pointer.next = new ListNode(l1.val + remain - 10);
remain = 1;
} else{
pointer.next = new ListNode(l1.val + remain);
remain = 0;
}
l1 = l1.next;
pointer = pointer.next;
} else{
if(l1.val + l2.val + remain >= 10){
pointer.next = new ListNode(l1.val + l2.val + remain - 10);
remain = 1;
} else{
pointer.next = new ListNode(l1.val + l2.val + remain);
remain = 0;
}
l1 = l1.next;
l2 = l2.next;
pointer = pointer.next;
}
}
if(remain == 1){
pointer.next = new ListNode(1);
}
return resultHead.next;
}
}