1 /**
 2 * Definition for singly-linked list.
 3 * struct ListNode {
 4 *     int val;
 5 *     struct ListNode *next;
 6 * };
 7 */
 8 struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {
 9     struct ListNode r = {0, NULL};          // 作為返回結果的頭結點
10     struct ListNode *p = &r;    //
 
 指針運算的p
11     
12     int flag = 0;               // 進位標誌
13   
14     while (l1 != NULL && l2 != NULL) {
15 
16         int tmp = l1->val + l2->val + flag;     // 如果都不為空則進行求和運算
17 
18         // 判斷是否有進位
19         if(tmp >= 10) {
20             flag = 1;
21             tmp = tmp % 10;
22         } else
 
 {
23             flag = 0;
24         }
25 
26         // 新增一個結點來r存儲值
27         struct ListNode * node = (struct ListNode *) malloc(sizeof(struct ListNode));
28         node->next = NULL;
29         node->val = tmp;
30         p->next = node;
31         p = p->next;
32 
33         l1 = l1->next;
 
34         l2 = l2->next;
35     }
36   
37     // 找到仍有結點的鏈表
38     struct ListNode *q;
39     if(l1 != NULL)
40         q = l1;
41     else
42         q = l2;
43   
44     while (q != NULL) {
45         int tmp = q->val + flag;
46 
47         if(tmp >= 10) {
48             flag = 1;
49             tmp = tmp % 10;
50         } else {
51             flag = 0;
52         }
53         struct ListNode * node = (struct ListNode *) malloc(sizeof(struct ListNode));
54         node->next = NULL;
55         node->val = tmp;
56         p->next = node;
57         p = p->next;
58     
59         q = q->next;
60     }
61   
62     if(flag == 1) {
63         struct ListNode * node = (struct ListNode *) malloc(sizeof(struct ListNode));
64         node->next = NULL;
65         node->val = flag;
66         p->next = node;
67         p=p->next;
68     }
69     
70     return r.next;
71 }                

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