[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;
	}
};