leetcode Add Two Numbers

题目

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

Java实现

/**
* 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) {
        int d = 0;
        ListNode head = new ListNode(0), l3 = head;

        while(l1 != null || l2 != null) {
            if(l1 != null) {
                d += l1.val;
                l1 = l1.next;
            }

            if(l2 != null) {
                d += l2.val;
                l2 = l2.next;
            }

            l3.next = new ListNode(d%10);
            l3 = l3.next;
            d = d/10;
        }

        if(d == 1) {
            ListNode n = new ListNode(1);
            l3.next = n;
        }

        return head.next;
    }
}

总结

1. 创建一个空的头结点简化操作；
2. 考虑最后一位进1。