c++ - Function moving list elements to the end of the list not working multiple times

Question

I need to make a function that moves the nth element in a singly linked list to the end of the list. I created some code that does that but it only works once if I try to do it again it moves the selected element to the end but the one that was moved previously gets deleted/dissapears. My theory is that it doesnt actually change the tail reference. so im stuck right now!

void move(int n)
    {
        if (head == NULL || head->next == NULL)
        {
            return;
        }
        node *first = head;
        node *temp =new node;

        for (int i = 1; i < n-1; i++)
        {
            first=first->next;
        }
        temp = first->next;
        first->next=first->next->next;
        temp->next = NULL;

        tail->next = temp;
        tail=temp;
    }

my input: 1 2 3 4 5

after moving the 3rd element for the first time:

1 2 4 5 3

after moving the 3rd element(4) for the 2nd time:

1 2 5 4

but it should be

1 2 5 3 4

标签： c++ooplinked-listnodessingly-linked-list

Answer 1

I checked your code with my own implementation. Your function move() is working fine. However, you should not be using 'new' in your 8th line of code as highlighted by @molbdnilo and @PaulMakenzie. But it is not responsible for this problem. There is a problem with some other part of your code.

#include<iostream>
using namespace std;

class List
{
    struct Node
    {
        int number;
        Node* next;
    };  

    Node* head;
    Node* tail;

    public:
    List()
    {
        head = NULL;
        tail = NULL;
    }
        void insert(int num)
    {
        Node* temp = new Node();
        temp->number = num;
        temp->next = NULL;

        if (head == NULL)
        {
            head = temp;
            tail = temp;
        }
        else
        {
            Node* point = head;
            while (point->next != NULL)
                point = point->next;

            point->next = temp;
            tail = point->next;
        }
    }
    void display()
    {
        Node* point = head;
        while (point != NULL)
        {
            cout << point->number << " ";
            point = point->next;
        }
    }

    void move(int n)
    {
        if (head == NULL || head->next == NULL)
        {
            return;
        }
        Node *first = head;
        Node *temp;

        for (int i = 1; i < n-1; i++)
        {
            first=first->next;
        }
        temp = first->next;
        first->next=first->next->next;
        temp->next = NULL;

        tail->next = temp;
        tail=temp;
    }
};

int main()
{
    List a;
    a.insert(1);
    a.insert(2);
    a.insert(3);
    a.insert(4);
    a.insert(5);

    a.move(3);
    a.move(3);

    a.display();

}