2-Add Two Numbers

问题描述：

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

 

注意一下有些特殊的测试用例：Input: [1], [9,9]       Input: [1,8], [0]        Input: [5], [5]        Input:   [0], [0]

 1 public class Solution {

 2 

 3 public ListNode addTwoNumbers(ListNode x, ListNode y) {

 4         int temp = 0;

 5         int pre = 0;

 6         int carry = 0;

 7         ListNode top = new ListNode(0);

 8         ListNode sum = top;

 9         while (x != null || y != null || carry != 0) {

10             if (x != null) {

11                 temp += x.val;

12                 x = x.next;

13             }

14             if (y != null) {

15                 temp += y.val;

16                 y = y.next;

17             }

18 

19             temp += carry;

20 

21             if (temp >= 10) {

22                 carry = 1;

23                 pre = temp % 10;

24                 temp = 0;

25             } else {

26                 carry = 0;

27                 pre = temp;

28                 temp = 0;

29             }

30             sum.val = pre;

31             if (carry != 0 || x != null || y != null) {

32                 sum.next = new ListNode(0);

33                 sum = sum.next;

34             }

35         }

36         return top;

37     }

38 }

View Code

注意一下进位，边界。跑了412 ms