LeetCode 002 Add Two Numbers - Java

Posted 2020-09-21

You are given two non-empty linked lists representing two non-negative integers. 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.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

 

定位：中等题

题意简单，两个倒置的非负整数，用链表存储，链表类的定义也给出：

public class ListNode {
　　int val;
　　ListNode next;
　　ListNode(int x) { val = x; }
}

 

现在要将这两数相加后得到的数也倒置用链表存储，因为已经倒置的缘故，低位在前，直接处理，不断向高位推进。

需要注意就是进位问题，当所有都处理完，最后还有进位存在，链表的最后还要加一个节点，值为1，即最高位为1.

 

Java实现：

 1 public class Solution {
 2     public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
 3         ListNode listNode=new ListNode(0);
 4         ListNode ptr1,ptr2,ptr;
 5         int addp=0;
 6         int now;
 7         ptr1=l1;
 8         ptr2=l2;
 9         ptr=listNode;
10         while (ptr1!=null&&ptr2!=null){
11             now=ptr1.val+ptr2.val+addp;
12             addp=0;
13             if(now>9){
14                 addp++;
15                 now-=10;
16             }
17             ptr.next=new ListNode(now);
18             ptr=ptr.next;
19             ptr1=ptr1.next;
20             ptr2=ptr2.next;
21         }
22         while (ptr1!=null){
23             now=ptr1.val+addp;
24             addp=0;
25             if(now>9){
26                 addp++;
27                 now-=10;
28             }
29             ptr.next=new ListNode(now);
30             ptr=ptr.next;
31             ptr1=ptr1.next;
32         }
33         while (ptr2!=null){
34             now=ptr2.val+addp;
35             addp=0;
36             if(now>9){
37                 addp++;
38                 now-=10;
39             }
40             ptr.next=new ListNode(now);
41             ptr=ptr.next;
42             ptr2=ptr2.next;
43         }
44         if(addp==1){
45             ptr.next=new ListNode(addp);
46         }
47         return listNode.next;
48     }
49 }