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;
}
};