ex13.28.cpp

class TreeNode
{
private:
    std::string value;
    int* count;
    TreeNode *left;
    TreeNode *right;
public:
    TreeNode()
        : value(std::string()), count(new int(1)),
        left(nullptr), right(nullptr) {}
    TreeNode(const TreeNode& rhs)
        : value(rhs.value), count(rhs.count), left(rhs.left), right(rhs.right) {}
    TreeNode& operator=(const TreeNode& rhs);
    ~TreeNode()
    {
        if (--*count == 0)
        {
            if (left)
            {
                delete left;
                left = nullptr;
            }
            if (right)
            {
                delete right;
                right = nullptr;
            }
            delete count;
            count = nullptr;
        }
    }
};

class BinStrTree
{
private:
    TreeNode *root;
public:
    BinStrTree() : root(new TreeNode()) {}
    BinStrTree(const BinStrTree& bst) : root(new TreeNode(*bst.root)) {}
    BinStrTree& operator=(const BinStrTree& bst);
    ~BinStrTree() {delete root;}
};

TreeNode& TreeNode::operator=(const TreeNode& rhs)
{
    ++*rhs.count;
    if (--*count == 0)
    {
        if (left)
        {
            delete left;
            left = nullptr;
        }
        if (right)
        {
            delete right;
            right = nullptr;
        }
        delete count;
        count = nullptr;
    }
    value = rhs.value;
    left = rhs.left;
    right = rhs.right;
    count = rhs.count;
    return *this;
}

BinStrTree& BinStrTree::operator=(const BinStrTree& bst)
{
    TreeNode* new_root = new TreeNode(*bst.root);
    delete root;
    root = new_root;
    return *this;
}