一.相关链接

题目链接：707.设计链表

二.心得体会

       这道题也是一道链表题，使用虚拟头节点来处理。整体的逻辑都是很简单的，需要注意的是判断索引值是否合理的时候，需要注意按索引增加链表节点时要比get和delete多一位，即>len。

三.代码

/*** Definition for singly-linked list.* struct ListNode {*     int val;*     ListNode *next;*     ListNode() : val(0), next(nullptr) {}*     ListNode(int x) : val(x), next(nullptr) {}*     ListNode(int x, ListNode *next) : val(x), next(next) {}* };*/class MyLinkedList {
public:struct ListNode {int val;ListNode *next;ListNode() : val(0), next(nullptr) {}ListNode(int x) : val(x), next(nullptr) {}ListNode(int x, ListNode *next) : val(x), next(next) {}};int _len;ListNode* _dummy_head;MyLinkedList() {_dummy_head = new ListNode(0);_len = 0;}int get(int index) {if(index<0||index>_len-1) return -1;ListNode* p = _dummy_head;for(int i=0;i<=index;i++){p = p->next;}int ans = p->val;return ans;}void addAtHead(int val) {ListNode* p = new ListNode(val);p->next = _dummy_head->next;_dummy_head->next = p;_len++;return ;}void addAtTail(int val) {ListNode* p = _dummy_head;ListNode* tail = new ListNode(val);for(int i=0;i<_len;i++){p = p->next;}p->next = tail;_len++;return ;}void addAtIndex(int index, int val) {if(index<0||index>_len) return;ListNode* p = _dummy_head;ListNode* index_node = new ListNode(val);for(int i=0;i<index;i++){p = p->next;}index_node->next = p->next;p->next = index_node;_len++;return ;}void deleteAtIndex(int index) {if(index<0||index>_len-1) return;ListNode* p = _dummy_head;for(int i=0;i<index;i++){p = p->next;}ListNode* tmp = p->next;p->next = tmp->next;delete tmp;_len--;return ;}
};/*** Your MyLinkedList object will be instantiated and called as such:* MyLinkedList* obj = new MyLinkedList();* int param_1 = obj->get(index);* obj->addAtHead(val);* obj->addAtTail(val);* obj->addAtIndex(index,val);* obj->deleteAtIndex(index);*/