LeetCode: Add Two Numbers 解题报告

Add Two Numbers
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

https://oj.leetcode.com/problems/add-two-numbers/

解答：

比较简单，直接用2个指针往后移动，并且将2个list的值相加，并且计算上carry值。注意，在while循环中加上carry == 1的判断，这样可以自动在链尾加上carry 的值。

 1 package Algorithms.list;

 2 

 3 import Algorithms.algorithm.others.ListNode;

 4 

 5 /**

 6  * Definition for singly-linked list.

 7  * public class ListNode {

 8  *     int val;

 9  *     ListNode next;

10  *     ListNode(int x) {

11  *         val = x;

12  *         next = null;

13  *     }

14  * }

15  */

16 public class AddTwoNumbers {

17     public static void main(String[] str) {

18         ListNode n1 = new ListNode(9);

19         

20         ListNode l1 = new ListNode(1);

21         ListNode l2 = new ListNode(9);

22         ListNode l3 = new ListNode(9);

23         ListNode l4 = new ListNode(9);

24         ListNode l5 = new ListNode(9);

25         ListNode l6 = new ListNode(9);

26         ListNode l7 = new ListNode(9);

27         ListNode l8 = new ListNode(9);

28         ListNode l9 = new ListNode(9);

29         ListNode l10 = new ListNode(9);

30         

31         l1.next = l2;

32         l2.next = l3;

33         l3.next = l4;

34         l4.next = l5;

35         l5.next = l6;

36         l6.next = l7;

37         l7.next = l8;

38         l8.next = l9;

39         l9.next = l10;

40         

41         System.out.println(addTwoNumbers(n1, l1).toString());

42     }

43     

44     public static ListNode addTwoNumbers(ListNode l1, ListNode l2) {

45         if (l1 == null || l2 == null) {

46             return null;

47         }

48         

49         ListNode dummy = new ListNode(0);

50         ListNode tail = dummy;

51         int carry = 0;

52         

53         while (l1 != null || l2 != null || carry == 1) {

54             int sum = carry;

55             if (l1 != null) {

56                 sum += l1.val;

57                 l1 = l1.next;

58             }

59             

60             if (l2 != null) {

61                 sum += l2.val;

62                 l2 = l2.next;

63             }

64             

65             carry = sum / 10;

66             

67             // create a new node and add it to the tail.

68             ListNode cur = new ListNode(sum % 10);

69             tail.next = cur;

70             tail = tail.next;

71         }

72         

73         return dummy.next;

74     }

75 }

View Code

 

代码：

AddTwoNumbers