[LeetCode]21. 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.

/**
* 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) {

}
};

本题没有说明合并后的链表也保证有序，代码如下：

//不考虑新链表的排序
class Solution{
public:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
ListNode *lhs = l1;
ListNode *rhs = lhs;
while (l1->next)
lhs = lhs->next;
lhs->next = l2;
return rhs;
}

};
//考虑新链表的排序
class Solution {
public:
ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
ListNode lhs(INT_MIN);
ListNode *rhs = &lhs;

while (l1 && l2) {
if (l1->val < l2->val) {
rhs->next = l1;
l1 = l1->next;
}
else {
rhs->next = l2;
l2 = l2->next;
}
rhs = rhs->next;
}

rhs->next = l1 ? l1 : l2;
return lhs.next;
}
};