LeetCode: Add Two Numbers 题解

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

 

题解： （1）注意处理进位问题。 （2） 注意两个链表长度不相等的时候。

 1 class Solution {

 2 public:

 3     ListNode *add(ListNode *l1, ListNode *l2,int c)

 4     {

 5         ListNode *head= new ListNode(0);

 6         if(l1==NULL && l2==NULL)

 7         {

 8             if(c==0)

 9                return NULL;

10             else

11             {

12                 head->val=1;

13                return head;

14             }

15         }

16         if(l1==NULL)

17             return add(head,l2,c);

18         if(l2==NULL)

19             return add(l1,head,c);

20 

21         if(l1!=NULL && l2!=NULL)

22         {

23            head->val =(l1->val + l2->val +c)%10;

24            c = (l1->val + l2->val +c)/10;

25            head->next = add(l1->next,l2->next,c);

26         }

27         return head;

28     }

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

30         int c=0;

31         if(l1==NULL) return l2;

32         if(l2==NULL) return l1;

33 

34         ListNode *head = add(l1,l2,c);

35         return head;

36     }

37 };

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