做題思路：

　　1，就考察了連結串列的基礎操作，題目要求什麼就照做就好了

 1 class MyLinkedList {
 2 public:
 3     struct LinkedList {   //甚至還先需要自己整一個連結串列的結構體，平時做題做慣了這裡會忘先弄結構體了
 4         int val;
 5         LinkedList* next;
 6         LinkedList(int val) : val(val), next(nullptr) {}
 7     };
 8     MyLinkedList() {
 9 
10     }
11     LinkedList* fakeNode = new
 
 LinkedList(0);  //經典虛擬頭節點，不知道為什麼如果把這行放到上面的建構函式裡面就識別不到，說未定義，真奇怪
12     int size = 0;  //為了檢測 index 是否合法
13     int get(int index) {
14         if (index > (size - 1) || index < 0)return -1;
15         LinkedList* cur = fakeNode;
16         while (index--) {
17             cur = cur->next;
18         }
 
19         return cur->next->val;
20     }
21     
22     void addAtHead(int val) {
23         LinkedList* cur = new LinkedList(val);
24         cur->next = fakeNode->next;
25         fakeNode->next = cur;
26         size++;
27     }
28     
29     void addAtTail(int val) {
30         LinkedList* cur = fakeNode;
 
31         while (cur->next != nullptr) {
32             cur = cur->next;
33         }
34         LinkedList* newNode = new LinkedList(val);
35         cur->next = newNode;
36         size++;
37     }
38     
39     void addAtIndex(int index, int val) {
40         if (index > size)return ;
41         LinkedList* cur = fakeNode;
42         while (index--) {
43             cur = cur->next;
44         }
45         LinkedList* newNode = new LinkedList(val);
46         newNode->next = cur->next;
47         cur->next = newNode;
48         size++;
49     }
50     
51     void deleteAtIndex(int index) {
52         if (index >= size || index < 0)return ;
53         LinkedList* cur = fakeNode;
54         while (index--) {
55             cur = cur->next;
56         }
57         LinkedList* temp = cur->next;
58         cur->next = cur->next->next;
59         delete temp;
60         size--;
61     }
62 };
63 
64 /**
65  * Your MyLinkedList object will be instantiated and called as such:
66  * MyLinkedList* obj = new MyLinkedList();
67  * int param_1 = obj->get(index);
68  * obj->addAtHead(val);
69  * obj->addAtTail(val);
70  * obj->addAtIndex(index,val);
71  * obj->deleteAtIndex(index);
72  */