Leetcode: Merge Two Sorted Lists

题目：

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

这道题和前面Leetcode: Merge Sorted Array 这道题看似类似，因为数据结构的不同，但是解法还是有一些不同的。

C++代码示例：

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution
{
public:
ListNode *mergeTwoLists(ListNode *l1, ListNode *l2)
{
//helper指向l1和l2指向最小的哪一个，一直循环着找下去
ListNode *helper = new ListNode(0);
ListNode *head = helper;
while (l1 && l2)
{
if (l1->val < l2->val)
{
helper->next = l1;
l1 = l1->next;
}
else
{
helper->next = l2;
l2 = l2->next;
}
helper = helper->next;
}
//如果最后l1或者l2还有指向的数据，直接接到helper的后面
if (l1) helper->next = l1;
if (l2) helper->next = l2;
return head->next;
}
};