算法DAY3|LC203.移除链表元素 707.设计链表 206.反转链表

206.移除链表元素

/**
 * 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 Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {
        if(head==nullptr){
            return head;
        }
        
        struct ListNode* dummyNode = new ListNode(0, head);
        struct ListNode* cur = dummyNode;

        while(cur->next!=nullptr){
            if(cur->next->val==val){
                cur->next=cur->next->next;
            }
            else{
                cur=cur->next;


            }
        }

        return dummyNode->next;

    }
};

思路很简单，注意声明dummyNode时要用Listnode的构造函数初始化，最后返回dummyNode->next才是头节点

206.反转链表

/**
 * 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 Solution {
public:
    ListNode* reverseList(ListNode* head) {

        

        ListNode* pre=nullptr;
        ListNode* cur=head;
        while(cur!=nullptr){
            ListNode* temp=cur->next;
            cur->next=pre;
            pre=cur;
            cur=temp;
        }

        return pre;

    }
};