letcode 分类练习 203.移除链表元素 707.设计链表 206.反转链表

移除链表元素

class Solution {
   
public:
    ListNode* removeElements(ListNode* head, int val) {
   
        ListNode* dummyhead = new ListNode();
        dummyhead -> next = head;
        ListNode* pre = dummyhead;
        while(head){
   
            if(head-> val == val){
   
                pre -> next = head -> next;
            }
            else{
   
                pre = head;
            }
            head = head -> next;
        }
        return dummyhead -> next;
    }
};

设计链表

关键是掌握链表结构体的定义和虚拟头结点

class MyLinkedList {
   
public:
    struct ListNode{
   
        ListNode* next;
        int val;
        ListNode(int _val){
   
            next = nullptr;
            val = _val;
        }
    };
    ListNode* d