算法分析与设计第二周

本周做了一题，题目如下：
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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

分析：重点在于两个链表长度不一致，还有进位问题，代码提交了很多次都没过，主要是细节问题，考虑问题还不完全。开始写的比较复杂，修修补补，导致比较长，最后重新写一遍，简练地解决了这个问题，代码如下：

/** * 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 *sum = new ListNode(0);        ListNode *current = sum;        int flag = 0;        while (l1 != NULL || l2 != NULL || flag)        {            int temp = (l1 ? l1->val : 0) + (l2 ? l2->val : 0) + flag;            l1 = l1 ? l1->next : l1;            l2 = l2 ? l2->next : l2;            flag = temp > 9 ? 1 : 0;            current->next = new ListNode(temp % 10);            current = current->next;        }        return sum->next;    }};