leetcode链表--14、add-two-numbers（两链表相加 得到新链表）

题目描述

 

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

 

解题思路：本题是将两个链表中的按照位进行相加形成一个新的链表。注意进位情况

本题在对题意理解时，出现错误，以为是将链表加完，然后倒序输出呢，导致未成功通过

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
        int flag = 0;//进位
        ListNode* tail = new ListNode(0);
        ListNode* ptr = tail;
 
        while(l1 != NULL || l2 != NULL)
        {
            int val1 = 0;
            if(l1 != NULL)
            {
                val1 = l1->val;
                l1 = l1->next;
            }
 
            int val2 = 0;
            if(l2 != NULL)
            {
                val2 = l2->val;
                l2 = l2->next;
            }
 
            int tmp = val1 + val2 + flag;
            ptr->next = new ListNode(tmp % 10);
            flag = tmp / 10;
            ptr = ptr->next;
        }
        //处理结束了flag还有一个进位则新申请一个为1的结点连入链表
        if(flag == 1)
        {
            ptr->next = new ListNode(1);
        }
        return tail->next;
    }
};