LinkedLists：变量自动更新，无需重新分配

Question

因此，发生的事情是，链表的头部在每次迭代中都得到了更新，这本不该发生，并且我无法对其进行调试。 任何帮助将不胜感激。

// Given arbitrarily big string with alphabet [ Implement using singly or doubly linked list ]
// Store the each alphabet into linked list

//  Example
//  Input:
// SSSKKBBBBHHHJJJJKKKK
// Store

这是问题（上）

#include <iostream>
#include <list>
#include <algorithm>

using namespace std;

class ListNode
{ //class for a node of the linked list
public:
    ListNode *next = NULL; //pointer to next node
    ListNode *prev = NULL; //pointer to previous node
    char data;             //the alphabet present in this node
    int frequency;         //number of times this alphabet is present in the list
    ListNode(char data)
    {
        this->data = data;
        frequency = 1;
    }
};

class LinkedList
{ //class for the entire linked list
public:
    ListNode **Head = NULL;
    ListNode **Tail = NULL;

    void printlist()
    {
        ListNode *temp = *Head;
        while (temp != NULL)
        {
            cout << temp->data << temp->frequency << " ";
            temp = temp->next;
        }
        return;
    }

    void insertNodeFromEnd(char c)
    {
        ListNode *newNode = new ListNode(c);
        cout << "input character: " << c << endl;
        if(Head != NULL){cout << "head = " << (*Head)->data << endl;}
        if (Head == NULL) //if the list is empty, point the head and tail to the node pointer of newly created node.
        {
            Head = &newNode;
            Tail = Head;
            cout << "empty condition: ";
            cout << "tail = " << (*Tail)->data << " ";
            cout << "head = " << (*Head)->data << endl;
        }
        else //else point the tail to pointer of newly created node.
        {
            {
                (*Tail)->next = newNode;
                Tail = &newNode;
                cout << "regular condition: ";
                cout << "tail = " << (*Tail)->data << " ";
                cout << "head = " << (*Head)->data << endl;
            }
        }
        return;
    }
};

这是主要功能

int main(int argc, char const *argv[])
{
    string s;
    cin >> s;
    int T;
    cin >> T;
    if (s.length() == 0)
    {
        cout << "Error! \n enter atleast one letter \n exiting...";
        return 0;
    }
    else
    {
        LinkedList listofalphabet;
        for (char &c : s)
        {
            listofalphabet.insertNodeFromEnd(c);
        }
    }
    return 0;
}