【C++】二叉树删除根节点出错！！求帮助解惑！！

Question

此代码可以正常删除叶子节点，但删除根节点时就出错。

出错截图如下

代码如下

#pragma once
#ifndef BT2
#define BT2
#include <iostream>
#include <queue>

template<class T>
class BT;

template<class T>
class Element
{
public:
    Element()
    {
        key = 0;
    }
    T key;
};

template<class T>
class BTNode
{
    friend class BT<T>;
private:
    BTNode()
    {
        data.key = 0;
        left = right = NULL;
    }
    Element<T> data;
    BTNode<T> *left;
    BTNode<T> *right;
    void display(int i)
    {
        std::cout << "Position " << i << ": data.key= " << data.key << "\n";
        if (left) left->display(2 * i);
        if (right) right->display(2 * i + 1);
    }
};
//二叉树类
template<class T>
class BT
{
public:
    BT(BTNode<T> *init = 0) :root(init) {};
    ~BT()
    {
        delete root;
    }
    void Insert(const Element<T> &x);
    void Search(const Element<T> &x);
    void InOrder();
    void PreOrder();
    void PostOrder();
    void LevelOrder();
    void Delete(const Element<T> &x);
    void visit(BTNode<T> *);
    void display()
    {
        std::cout << "\n";
        if (root)
        {
            std::cout << "根为：" << root->data.key << "\n";
            root->display(1);
        }
        else
        {
            std::cout << "This is a empty tree!" << "\n";
        }
    }
    BTNode<T> *miniMum(BTNode<T> *);
    BTNode<T> *RemoveMin(BTNode<T> *);
private:
    BTNode<T> *root;
    void InOrder(BTNode<T> *a);
    void PreOrder(BTNode<T> *a);
    void PostOrder(BTNode<T> *a);
    BTNode<T> *Delete(BTNode<T> *, const Element<T> &);
};

//二叉树结点类
template<class T>
BTNode<T> *BT<T>::miniMum(BTNode<T> *a)
{
    if (a->left == NULL)
    {
        return a;
    }
    a->left = miniMum(a->left);
    return a;
}

template<class T>
BTNode<T> *BT<T>::RemoveMin(BTNode<T> *a)
{
    if (a->left == NULL)
    {
        BTNode<T> *leftnode1 = a->right;
        delete a;
        return leftnode1;
    }
    a->left = RemoveMin(a->left);
    return a;
}


template<class T>
void BT<T>::visit(BTNode<T> *a)
{
    std::cout << a->data.key << " ";
}

//插入节点
template<class T>
void BT<T>::Insert(const Element<T> &x)
{
    BTNode<T> *p = root;
    BTNode<T> *q = 0;
    while (p)
    {
        q = p;
        if (x.key == p->data.key) return;
        else if (x.key < p->data.key)
        {
            p = p->left;
        }
        else
        {
            p = p->right;
        }

    }
    p = new BTNode<T>;
    p->data.key = x.key;
    if (!root) root = p;
    else if (x.key < q->data.key) q->left = p;
    else q->right = p;


}

//查找节点
template<class T>
void BT<T>::Search(const Element<T> &x)
{
    BTNode<T> *current = root;
    bool a = false;
    while (current)
    {
        if (x.key == current->data.key)
        {
            a = true;
            std::cout << "已找到！" << "\n";
            break;
        }
        else if (x.key < current->data.key)
        {
            current = current->left;
        }
        else
        {
            current = current->right;
        }
    }
    if (!a)
    {
        if (current == root)
        {
            std::cout << "树为空！" << "\n";
        }
        else
        {
            std::cout << "未找到！" << "\n";
        }

    }
}

//中序遍历
template<class T>
void BT<T>::InOrder()
{
    InOrder(root);
}
template<class T>
void BT<T>::InOrder(BTNode<T> *a)
{
    if (a->left) InOrder(a->left);
    visit(a);
    if(a->right) InOrder(a->right);

}

//前序遍历
template<class T>
void BT<T>::PreOrder()
{
    PreOrder(root);
}
template<class T>
void BT<T>::PreOrder(BTNode<T> *a)
{
    visit(a);
    if (a->left) PreOrder(a->left);
    if (a->right) PreOrder(a->right);
}

//后序遍历
template<class T>
void BT<T>::PostOrder()
{
    PostOrder(root);
}
template<class T>
void BT<T>::PostOrder(BTNode<T> *a)
{
    visit(a);
    if (a->left) PostOrder(a->left);
    if (a->right) PostOrder(a->right);
}

//层序遍历
template<class T>
void BT<T>::LevelOrder()
{
    std::queue<BTNode<T> *> b;
    BTNode<T> *a = root;
    while (a)
    {
        visit(a);
        if (a->left) b.push(a->left);
        if (a->right) b.push(a->right);
        if (b.empty()) return;
        a = b.front();
        b.pop();
    }
}

//删除节点
template<class T>
void BT<T>::Delete(const Element<T> &x)
{
    if (root)
    {
        root = Delete(root, x);
    }
}
template<class T>
BTNode<T> *BT<T>::Delete(BTNode<T> *a, const Element<T> &x)
{
    if (a == NULL) return NULL;
    if (x.key < a->data.key)
    {
        a->left = Delete(a->left, x);
        return a;
    }
    else if (x.key > a->data.key)
    {
        a->right = Delete(a->right, x);
        return a;
    }
    else
    {
        if (a->left == NULL)
        {
            BTNode<T> *rightnode = a->right;
            delete a;
            return rightnode;
        }
        if (a->right == NULL)
        {
            BTNode<T> *leftnode = a->left;
            delete a;
            return leftnode;
        }
    }
    BTNode<T> *dela = a;
    BTNode<T> *successor = miniMum(a->right);
    successor->left = a->left;
    successor->right = RemoveMin(a->right);
    delete dela;
    return successor;

}
#endif // !BT2

#include "树2.h"

int main()
{
    Element<int> a, b, c, d, e, f;
    a.key = 5;
    b.key = 8;
    c.key = 12;
    d.key = 1;
    e.key = 3;
    f.key = 24;
    BT<int> m;
    m.Insert(a);
    m.Insert(b);
    m.Insert(c);
    m.Insert(d);
    m.Insert(e);
    m.Delete(a);**//删除b节点时正常运行，删除根节点（a）时出错！**
    m.display();


    return 0;
}

Answer 1

二叉树的根节点不能删，只能更新值，我博客里有类似于完全二叉树的排序算法