21.合并两个有序链表.cpp

/*
 * @lc app=leetcode.cn id=21 lang=cpp
 *
 * [21] 合并两个有序链表
 *
 * https://leetcode-cn.com/problems/merge-two-sorted-lists/description/
 *
 * algorithms
 * Easy (56.46%)
 * Likes:    581
 * Dislikes: 0
 * Total Accepted:    99.2K
 * Total Submissions: 175.2K
 * Testcase Example:  '[1,2,4]\n[1,3,4]'
 *
 * 将两个有序链表合并为一个新的有序链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。 
 * 
 * 示例：
 * 
 * 输入：1->2->4, 1->3->4
 * 输出：1->1->2->3->4->4
 * 
 * 
 */

// @lc code=start
/**
 * 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) {
        ListNode *l3 = new ListNode(-1);
        ListNode *p = l3;
        while (l1 != NULL && l2 != NULL) {
            if (l1->val < l2->val) {
                p->next = l1;
                l1 = l1->next;
            } else {
                p->next = l2;
                l2 = l2->next;
            }
            p->next->next = NULL;
            p = p->next;
        }
        p->next = l1 != NULL ? l1 : l2;
        return l3->next;
    }
};
// @lc code=end