合并两个有序链表

21. 合并两个有序链表

将两个升序链表合并为一个新的 升序 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 1：

输入：l1 = [1,2,4], l2 = [1,3,4]
输出：[1,1,2,3,4,4]

示例 2：

输入：l1 = [], l2 = []
输出：[]

示例 3：

输入：l1 = [], l2 = [0]
输出：[0]

 

提示：

  • 两个链表的节点数目范围是 [0, 50]
  • -100 <= Node.val <= 100
  • l1 和 l2 均按 非递减顺序 排列

解法1最笨的解法：

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode() : val(0), next(nullptr) {}
 7  *     ListNode(int x) : val(x), next(nullptr) {}
 8  *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 9  * };
10  */
11 class Solution {
12 public:
13     void insertNodeAtTail(ListNode *&head, int val) {
14         ListNode *newNode = new ListNode(val);
15         ListNode *currentNode = head;
16         if (head == nullptr) {
17             head = newNode;
18             return;
19         }
20         while (currentNode->next != nullptr) {
21             currentNode = currentNode->next;
22         }
23         currentNode->next = newNode;
24         return;
25     }
26 
27     ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
28         if (list1 == nullptr && list2 == nullptr) {
29             return nullptr;
30         }
31         vector<int> vec;
32         while (list1 != nullptr) {
33             vec.push_back(list1->val);
34             list1 = list1->next;
35         }
36         while (list2 != nullptr) {
37             vec.push_back(list2->val);
38             list2 = list2->next;
39         }
40         sort(vec.begin(), vec.end());
41         ListNode *newHead = nullptr;
42         for (const auto &v : vec) {
43             insertNodeAtTail(newHead, v);
44         }
45         return newHead;
46     }
47 };

解法二（两个链表按照先拼接较小的）：

 1 #include <iostream>
 2 #include <vector>
 3 
 4 using namespace std;
 5 
 6 class ListNode {
 7 public:
 8     ListNode() : val(0), next(nullptr) {}
 9     ListNode(int x) : val(x), next(nullptr) {}
10     ListNode(int x, ListNode *next) : val(x), next(next) {}
11 
12 public:
13     int val;
14     ListNode *next;
15 };
16 
17 class Solution {
18 public:
19     ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) { // 合并两个有序链表
20         ListNode *dummyNode = new ListNode(0);
21         ListNode *currentNode = dummyNode;
22         ListNode *newHead = nullptr;
23         while (list1 != nullptr && list2 != nullptr) {
24             if (list1->val <= list2->val) {
25                 currentNode->next = list1;
26                 list1 = list1->next;
27             } else {
28                 currentNode->next = list2;
29                 list2 = list2->next;
30             }
31             currentNode = currentNode->next;
32         }
33         if (list1 != nullptr) {
34             currentNode->next = list1;
35         } else {
36             currentNode->next = list2;
37         }
38         newHead = dummyNode->next;
39         delete dummyNode;
40         return newHead;
41     }
42     // 尾插法插入链表元素
43     void insertNodeAtTail(ListNode *&head, int val) {
44         ListNode *newNode = new ListNode(val);
45         ListNode *currentNode = head;
46         if (head == nullptr) {
47             head = newNode;
48             return;
49         }
50         while (currentNode->next != nullptr) {
51             currentNode = currentNode->next;
52         }
53         currentNode->next = newNode;
54         return;
55     }
56     // 打印链表元素
57     void printfListNode(ListNode *head) {
58         while (head != nullptr) {
59             std::cout << head->val << "->";
60             head = head->next;
61         }
62         std::cout << "NULL" << endl;
63         return;
64     }
65 };
66 int main()
67 {
68     Solution *test = new Solution();
69     vector<int> vec1 = {1, 2, 4 };
70     ListNode *list1 = nullptr;
71     // 插入节点
72     for (const auto &v : vec1) {
73         test->insertNodeAtTail(list1, v);
74     }
75     test->printfListNode(list1); // 1->2->4->NULL
76 
77     vector<int> vec2 = {1, 3, 4 };
78     ListNode *list2 = nullptr;
79     // 插入节点
80     for (const auto &v : vec2) {
81         test->insertNodeAtTail(list2, v);
82     }
83     test->printfListNode(list2); // 1->3->4->NULL
84 
85     ListNode *mergedNewHead = test->mergeTwoLists(list1, list2);
86     test->printfListNode(mergedNewHead); // 1->1->2->3->4->4->NULL
87 
88     delete test;
89     system("pause");
90     return 0;
91 }

运行结果：

 

 

posted @ 2022-03-02 00:01  跳动的休止符  阅读(30)  评论(0)    收藏  举报