一、题目

二、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 Solution {
    
public:
    ListNode* reverseList(ListNode* head) {
    
    
   //题目分析:

    //Unified linked list format
    ListNode* dummyhead = new ListNode(0);  //Set a fake header node In order to unify the single-node and multi-node situations 
    dummyhead->next = head;

    //current and previous
    ListNode* first_node = new ListNode(0); 
    first_node=head;

    ListNode* second_node = new ListNode(0); 
    second_node=head;

    ListNode* temp_node = new ListNode(0); 
    temp_node=nullptr;

    if(head!=nullptr)
    temp_node=head->next;
  
   //第一个节点指向空
    if(head!=nullptr)
    head->next=nullptr;

   // Node for stepping Nodes and pointers are still different
    while(temp_node!=nullptr)
     {
    
        first_node=temp_node; 
        temp_node=first_node->next;       //before the last steptemp都记录
        std::cout<<" second1 "<<second_node->val<<std::endl; 
        first_node->next=second_node;
        second_node=first_node;
        std::cout<<" first "<<first_node->val<<std::endl;
        std::cout<<" second2 "<<second_node->val<<std::endl; 
     }

        // ListNode *show_node;
        // show_node=first_node; //Construct a display node
        // while(show_node->next!=nullptr)
        // {
    
        // std::cout<<" "<<show_node->val<<" ";
        // show_node=show_node->next;
        // }
        // std::cout<<" "<<show_node->val<<" "; //打印最后一个
        // std::cout<<" "<< std::endl;


    
    return first_node;
    }
};

三、运行结果