Add Two Numbers

Description:

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

Definition for singly-linked list:

struct ListNode {

      int val;

      ListNode *next;

      ListNode(int x) : val(x), next(NULL) {}

 };

Code:

 1  ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {

 2         size_t lengthL1 = 0;

 3         size_t lengthL2 = 0;

 4         ListNode *result = NULL;

 5         ListNode *pL1 = l1;

 6         ListNode *pL2 = l2;

 7         while (pL1)

 8         {

 9             lengthL1++;

10             pL1 = pL1->next;

11         }

12         while (pL2)

13         {

14             lengthL2++;

15             pL2 = pL2->next;

16         }

17         

18         ListNode *longList = (lengthL1 >= lengthL2)?l1:l2;

19         ListNode *shortList = (lengthL1 < lengthL2)?l1:l2;

20         

21         //设置进位标志

22         int flag = 0;

23         int x;

24         ListNode *p = NULL;

25         while (shortList)

26         {

27             x = flag + longList->val + shortList->val;

28             flag = x/10;

29             if (result==NULL)

30             {

31                 result = new ListNode ( x%10 );

32                 p = result;

33             }

34             else

35             {

36                 p->next = new ListNode (x%10);

37                 p = p->next;

38             }

39             shortList = shortList->next;

40             longList = longList->next;

41         }

42          while (longList)

43         {

44             if (flag == 0)

45             {

46                    p->next = longList; 

47                    return result;

48             }

49             else

50             {

51                 x = flag + longList->val;

52                 flag = x/10;

53                 p->next = new ListNode (x%10);

54                 p = p->next;

55                 longList = longList->next;

56              }

57         }

58             if (flag==1)

59             {

60                 p->next = new ListNode (1);

61             }

62             return result;

63     }