[leetCode]Add Two Numbers

想当初写过C的大数加减法，恍如隔世。
 1 #include <iostream>
 2 using namespace std;
 3 struct ListNode {
 4     int val;
 5     ListNode *next;
 6     ListNode(int x) : val(x), next(NULL) {}
 7 };
 8 class Solution {
 9 public:
10     ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
11         if(l1 == NULL) return l2;
12         if(l2 == NULL) return l1;
13         ListNode *head,*tail;
14         head = tail = NULL;
15         bool isCarry = false;
16         while(l1 != NULL && l2 != NULL){
17             int digit = l1->val + l2->val;
18             if(isCarry) digit++;
19             if(digit >= 10){
20                 digit %= 10;
21                 isCarry = true;
22             }else{
23                 isCarry = false;
24             }
25             if(head == NULL) head = tail = new ListNode(digit);
26             else{
27                 tail->next = new ListNode(digit);
28                 tail = tail->next;
29             }
30             l1 = l1->next;
31             l2 = l2->next;
32         }
33         ListNode *cur = NULL;
34         if(l1 == NULL && l2 == NULL){
35             if(isCarry) tail->next = new ListNode(1);
36             return head;
37         }
38         else if(l1 == NULL) cur = l2;
39         else if(l2 == NULL) cur = l1;
40         tail->next = cur;
41         while(isCarry){
42             cur->val +=1;
43             if(cur->val < 10) isCarry = false;
44             else{
45                 cur->val %= 10;
46                 if(cur->next == NULL) cur->next = new ListNode(0);
47                 cur = cur->next;
48             }
49         }
50         return head;
51     }
52 };
艰难的成长