LeetCode: Add two numbers

这题没什么难度，直接看代码吧

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode* dfs(ListNode *l1, ListNode *l2, int carry) {
12         if (!l1 && !l2) {
13             if (!carry) return NULL;
14             else {
15                 ListNode* tmp = new ListNode(carry);
16                 return tmp;
17             }
18         }
19         if (!l1) {
20             int sum = l2->val + carry;
21             ListNode* tmp = new ListNode(sum%10);
22             carry = sum/10;
23             tmp->next = dfs(l1, l2->next, carry);
24             return tmp;
25         }
26         if (!l2) {
27             int sum = l1->val + carry;
28             ListNode* tmp = new ListNode(sum%10);
29             carry = sum/10;
30             tmp->next = dfs(l1->next, l2, carry);
31             return tmp;
32         }
33         if (l1 && l2) {
34             int sum = l1->val + l2->val + carry;
35             ListNode* tmp = new ListNode(sum%10);
36             carry = sum/10;
37             tmp->next = dfs(l1->next, l2->next, carry);
38             return tmp;
39         }
40     }
41     ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
42         // Start typing your C/C++ solution below
43         // DO NOT write int main() function
44         int carry = 0;
45         ListNode *ret = dfs(l1, l2, carry);
46         return ret;
47     }
48 };

Java：

 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) { val = x; }
 7  * }
 8  */
 9 public class Solution {
10     public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
11         return addTwoNumbersWithCarry(l1, l2, 0);
12     }
13     private ListNode addTwoNumbersWithCarry(ListNode l1, ListNode l2, int carry)
14     {
15         if (l1 == null && l2 == null) 
16         {
17             if (carry > 0)
18             {
19                 return new ListNode(carry);
20             }
21             else
22             {
23                 return null;
24             }
25         }
26         else if (l1 == null)
27         {
28             int num = l2.val + carry;
29             ListNode newNode = new ListNode(num % 10);
30             newNode.next = addTwoNumbersWithCarry(l1, l2.next, num / 10);
31             return newNode;
32         }
33         else if (l2 == null)
34         {
35             int num = l1.val + carry;
36             ListNode newNode = new ListNode(num % 10);
37             newNode.next = addTwoNumbersWithCarry(l1.next, l2, num / 10);
38             return newNode;
39         }
40         else
41         {
42             int num = l1.val + l2.val + carry;
43             ListNode newNode = new ListNode(num % 10);
44             newNode.next = addTwoNumbersWithCarry(l1.next, l2.next, num / 10);
45             return newNode;
46         }
47     }
48 }