题目描述(Easy)

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.

题目链接

https://leetcode.com/problems/merge-two-sorted-lists/description/

Example 1:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

算法分析

创建一个头结点，从前往后合并。

提交代码：

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