leetcode-【中等題】2. Add Two Numbers

題目

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

連接

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

答案

一、直接按順序加就行，保存進位carry

二、到最後還須要考慮進位carry是否爲0

代碼

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
12         if(l1 == NULL)
13         {
14             return l2;
15         }
16         
17         if(l2 == NULL)
18         {
19             return l1;
20         }
21         
22         ListNode *ans = NULL;
23         ListNode *point = NULL;
24         int carry = 0;
25         int sum = 0;
26         while(l1 != NULL && l2 != NULL)
27         {
28             sum = carry + l1->val + l2->val;
29             carry = sum / 10;
30             sum = sum % 10;
31             
32             ListNode *value = new ListNode(sum);
33             if(ans == NULL)
34             {
35                 ans = value;
36             }
37             
38             if(point != NULL)
39             {
40                 point->next = value;
41             }
42             point = value;
43             
44             l1 = l1->next;
45             l2 = l2->next;
46         }
47         
48         while(l1 != NULL)
49         {
50             sum = carry + l1->val;
51             carry = sum / 10;
52             sum = sum % 10;
53             ListNode *value = new ListNode(sum);
54             point->next = value;
55             point = value;
56             
57             l1 = l1->next;
58         }
59         
60         while(l2 != NULL)
61         {
62             sum = carry + l2->val;
63             carry = sum / 10;
64             sum = sum % 10;
65             ListNode *value = new ListNode(sum);
66             point->next = value;
67             point = value;
68             
69             l2 = l2->next;
70         }
71         
72         if(carry != 0)
73         {
74             ListNode *value = new ListNode(carry);
75             point->next = value;
76             point = value;
77         }
78         
79         return ans;
80     }
81 };

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