题目

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.

思路分析

没啥好说的，指针操作，水题。时间太晚了，一边看S9一边写，效率低下。

我的代码

/**
 * 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 len_1 = 0, len_2 = 0;
        ListNode *r1 = l1, *r2 = l2, *l3 = new ListNode(-1), *r3 = l3;;
        int former = 0, x1, x2;
        while (r1 != NULL || r2 != NULL) {
            x1 = r1 == NULL ? 0 : r1->val;
            x2 = r2 == NULL ? 0 : r2->val;
            l3->val = (x1 + x2 + former) % 10;
            former = int((x1 + x2 + former) / 10);
            ListNode *l3_next = new ListNode(-1);
            l3->next = l3_next;
            l3 = l3->next;
            if (r1)
                r1 = r1->next;
            if (r2)
                r2 = r2->next;
        }
        if (former) {
            l3->val = former;
        }
        l3 = r3;
        while (r3 != NULL) {
            if (r3->next != NULL && r3->next->val == -1) {
                r3->next = NULL;
                break;
            }
            r3 = r3->next;
        }
        return l3;
    }
};