学步园

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

感觉这题目没啥难度可言。

/**
 * 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 *result = new ListNode(0);
        ListNode *pre = result;
        int carry = 0;

        while (l1 || l2) {
                if (l1) {
                        carry += l1->val;
                        l1 = l1->next;
                }

                if (l2) {
                        carry += l2->val;
                        l2 = l2->next;
                }

                if (carry > 9) {
                        pre->next = new ListNode(carry - 10);
                        carry = 1;
                }
                else {
                        pre->next = new ListNode(carry);
                        carry = 0;
                }
                pre = pre->next;
        }

        if (carry) {
                pre->next = result;
                pre = result->next;
                result->next = 0;
                result->val = carry;
        }
        else {
                pre = result->next;
                delete result;
        }

        return pre;
    }
};