使用模板和unique_ptr实现的二叉搜索树中返回具有最小值的节点

Question

我正在尝试与unique_ptr实现BST。我想用BST中的最小值返回节点。我知道如何返回最小值，我为它写了函数，但如果我想返回节点怎么办?我上的课有可能吗?

#include <iostream>
#include <memory>
template<class T>
class BinarySearchTree{
    struct TreeNode;
    typedef std::unique_ptr<TreeNode> spTreeNode;
    struct TreeNode{
        T data;
        spTreeNode  left;
        spTreeNode  right;
        TreeNode(const T & value):data(value),left(nullptr),right(nullptr){}
    };

    spTreeNode root;
    bool insert(spTreeNode &node);
    void print(const spTreeNode&) const ;
public:
    BinarySearchTree();
    void insert( const T & node);
    void print()const;
    T getMin();
};
template<class T>
BinarySearchTree<T>::BinarySearchTree():root(nullptr){}
template<class T>
void BinarySearchTree<T>::insert(const T & ref)
{
    std::unique_ptr<TreeNode> node(new TreeNode(ref));
    if (root == nullptr) {
        root = std::move(node);
    } else {
        TreeNode* temp = root.get();
        TreeNode* prev = root.get();
        while (temp != nullptr) {
            prev = temp;
            if (temp->data < ref)
                temp = temp->right.get();
            else
                temp = temp->left.get();
        }
        if (prev->data < ref)
            prev->right = std::move(node);
        else
            prev->left = std::move(node);
    }
}

template<class T>
T BinarySearchTree<T>::getMin()
{
    TreeNode* temp = root.get();
    TreeNode *prev = nullptr;
    while (temp)
    {
        prev = temp;
        temp = temp->left.get();
    }
    return prev->data;
}

int main()
{
    BinarySearchTree<int> bst;
    bst.insert(13);
    bst.insert(3);
    bst.insert(5);
    bst.insert(31);
    bst.insert(511);
    bst.insert(311);
    std::cout << bst.getMin(); // Works but what if I want to return the Node?
    return 0;
}

Answer 1

您必须决定您想要的接口。是否要返回一个指向现有TreeNode的const指针?对TreeNode的const引用?TreeNode的副本?关键是要考虑引用/指针的有效期。

坦率地说，我不认为这些都是公共接口的好主意。假设您将getMinNode()设置为私有，并将getMin()设置为公共:

// Returns non-owning pointer; do not attempt to delete TreeNode.
template<class T>
const BinarySearchTree<T>::TreeNode* BinarySearchTree<T>::getMinNode() const
{
    // Like getMin(), but return prev
    // Does this work for empty BinarySearchTree?
    TreeNode* temp = root.get();
    TreeNode *prev = nullptr;
    while (temp)
    {
        prev = temp;
        temp = temp->left.get();
    }
    return prev;
}
template<class T>
T BinarySearchTree<T>::getMin() const   // member function is const
{
    return getMinNode()->data;
}