Add two numbers leetcode

 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     if (l1 == NULL)
10         return l2;
11     if (l2 == NULL)
12         return l1;
13     struct ListNode*p1 = l1, *p2 = l2, *pNew = NULL,*pre=p1;
14     int res, carry = 0;
15     while (p1&&p2)
16     {
17         res = p1->val + p2->val + carry;
18         carry = res / 10;
19         p1->val = res % 10;
20         pre = p1;
21         p1 = p1->next;
22         p2 = p2->next;
23     }
24     if (p2 != NULL)
25     {
26         pre->next = p2;
27         while (p2)
28         {
29             res = (p2->val + carry);
30             p2->val = res % 10;
31             carry = res / 10;
32             pre=p2;
33             p2 = p2->next;
34             if(p2==NULL&&carry==1)//一定要考虑这种进位了的情况
35             {
36                 pNew=malloc(sizeof(struct ListNode));
37                 pNew->val=1;
38                 pNew->next=NULL;
39                 pre->next=pNew;
40             }
41                 
42         }
43     }
44     else if (p1 != NULL)
45     {
46         while (p1)
47         {
48             res = p1->val + carry;
49             p1->val = res % 10;
50             carry = res / 10;
51             pre=p1;
52             p1 = p1->next;
53             if(p1==NULL&&carry==1)
54             {
55                 pNew=malloc(sizeof(struct ListNode));
56                 pNew->val=1;
57                 pNew->next=NULL;
58                 pre->next=pNew;
59             }
60         }
61     }
62     else
63     {
64         if (carry == 1)
65         {
66             pNew =malloc(sizeof(struct ListNode));
67             pNew->val = carry;
68             pNew->next = NULL;
69             pre->next = pNew;
70         }
71     }
72     return l1;
73 
74 }