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* swapPairs(ListNode* head)
    {
    
     
    // //统一链表格式
    // ListNode* dummyhead = new ListNode(0); //设置虚假的头结点 为了使得单节点和多节点情况统一 
    // dummyhead->next = head;

    ListNode* test_node = new ListNode(0);    //探测节点 Check to see if there are more than two nodes after that
    test_node=head;

    if(test_node==nullptr) return test_node;   //空节点直接返回
    else if(test_node->next==nullptr) return test_node;  //A single node is returned directly
    else                                       //大于两个节点 开始操作 比如 2 1 null 
    {
    

    ListNode* return_node = new ListNode(0); 
    return_node=head->next;

    ListNode* temp_node = new ListNode(0);      //两大类情况 If there is no node in the linked list or there is only one node Then it should return directly ***最核心部分 Sentinel detection
    ListNode* quick_node = new ListNode(0); 
    ListNode* slow_node = new ListNode(0); 
    


    temp_node=head->next->next;
    quick_node=head->next;
    slow_node=head;

    int one_opeation=0;

    while(test_node!=nullptr&&test_node->next!=nullptr)
    {
    
        std::cout<<" 进入 "<<std::endl;
        // //Used to display the current node value
        // std::cout<<"slow_node->val "<<slow_node->val <<std::endl;
        // std::cout<<"quick_node->val "<<quick_node->val <<std::endl;
        // std::cout<<"temp_node->val "<<temp_node->val <<std::endl;

        test_node=test_node->next->next;  // Each round of the probe pointer operates independently

    

       if(one_opeation==1)
       {
    
       slow_node=temp_node;
       quick_node=slow_node->next;
       temp_node=quick_node->next;
       }

        if(one_opeation==0) one_opeation=1;   //The first round is not required

       quick_node->next=slow_node;

       //temp_nodeThere are three situations when moving down nullprt 一个值 两个值
       if(temp_node==nullptr)         slow_node->next=temp_node;
       else if (temp_node!=nullptr&&temp_node->next==nullptr)   slow_node->next=temp_node;
       else if(temp_node!=nullptr&&temp_node->next!=nullptr)    slow_node->next=temp_node->next;
 
       

            // //Used to display the current linked list
            // ListNode *show_node;
            // show_node=return_node; //构造处理节点
            // 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;

        // //Used to display the current node value
        // std::cout<<"slow_node->val "<<slow_node->val <<std::endl;
        // std::cout<<"quick_node->val "<<quick_node->val <<std::endl;
        // std::cout<<"temp_node->val "<<temp_node->val <<std::endl;

      std::cout<<" 离开 "<<std::endl;
    }
    return return_node;
    }

    }
};

三、运行结果