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

从链表头部向尾部逐一相加，注意进位即可。

实现代码

// Runtime: 40 ms
/**
 * 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) {
        ListNode *newHead = new ListNode(0);
        ListNode *temp = newHead;
        int sum = 0;
        while (l1 != NULL || l2 != NULL)
        {
            if (l1 != NULL)
            {
                sum += l1->val;
                l1 = l1->next;
            }
            if (l2 != NULL)
            {
                sum += l2->val;
                l2 = l2->next;
            }

            temp->next = new ListNode(sum % 10);
            temp = temp->next;
            sum /= 10;
        }

        if (sum == 1)
        {
            temp->next = new ListNode(sum);
        }

        return newHead->next;
    }
};