2. Add Two Numbers

Posted 2020-10-20 followyounger

---

You are given two non-empty linked lists representing two non-negative integers. 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.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

这个题目就是求和，但是要考虑进位问题。

 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* addTwoNumbers(ListNode* l1, ListNode* l2) {
12         ListNode head(0);
13         ListNode* pre = &head;
14         if(!l1)return l2;
15         if(!l2)return l1;
16         int extra = 0;
17         while(l1||l2||extra){
18             if(l1){
19                 extra += l1->val;
20                 l1 = l1->next;
21             }
22             if(l2){
23                 extra += l2->val;
24                 l2 = l2->next;
25             }
26             pre->next = new ListNode(extra%10);
27             extra = extra/10;
28             pre = pre->next;
29         }
30         return head.next;
31     }
32 };