【C++航海王：追寻罗杰的编程之路】一篇文章带你了解二叉搜索树

#pragma once
#include <iostream>
using namespace std;

template<class K>
struct BSTreeNode
{
	BSTreeNode<K>* _left;
	BSTreeNode<K>* _right;
	K _key;

	BSTreeNode(const K& key)
		:_left(nullptr)
		, _right(nullptr)
		, _key(key)
	{}
};

template<class K>
class BSTree
{
	typedef BSTreeNode<K> Node;
public:
	bool Insert(const K& key)
	{
		if (_root == nullptr)
		{
			_root = new Node(key);
			return true;
		}

		Node* parent = nullptr;
		Node* cur = _root;
		while (cur)
		{
			parent = cur;
			if (cur->_key < key)
			{
				cur = cur->_right;
			}
			else if (cur->_key > key)
			{
				cur = cur->_left;
			}
			else
			{
				return false;
			}
		}

		cur = new Node(key);
		if (parent->_key < key)
		{
			parent->_right = cur;
		}
		else
		{
			parent->_left = cur;
		}

		return true;
	}

	bool Find(const K& key)
	{
		Node* cur = _root;
		while (cur)
		{
			if (cur->_key < key)
			{
				cur = cur->_right;
			}
			else if (cur->_key > key)
			{
				cur = cur->_left;
			}
			else
			{
				return true;
			}
		}

		return false;
	}

	bool Erase(const K& key)
	{
		Node* parent = nullptr;
		Node* cur = _root;
		while (cur)
		{
			if (cur->_key < key)
			{
				parent = cur;
				cur = cur->_right;
			}
			else if (cur->_key > key)
			{
				parent = cur;
				cur = cur->_left;
			}
			else
			{
				// 准备删除
				if (cur->_left == nullptr)
				{//左为空
					if (cur == _root)
					{
						_root = cur->_right;
					}
					else
					{
						if (cur == parent->_left)
						{
							parent->_left = cur->_right;
						}
						else
						{
							parent->_right = cur->_right;
						}
					}

					delete cur;
				}
				else if (cur->_right == nullptr)
				{//右为空
					if (cur == _root)
					{
						_root = cur->_left;
					}
					else
					{
						if (cur == parent->_left)
						{
							parent->_left = cur->_left;
						}
						else
						{
							parent->_right = cur->_left;
						}
					}

					delete cur;
				}
				else
				{//左右都不为空

					// 右树的最小节点(最左节点)
					Node* parent = cur;
					Node* subLeft = cur->_right;
					while (subLeft->_left)
					{
						parent = subLeft;
						subLeft = subLeft->_left;
					}

					swap(cur->_key, subLeft->_key);

					if (subLeft == parent->_left)
						parent->_left = subLeft->_right;
					else
						parent->_right = subLeft->_right;

					delete subLeft;
				}

				return true;
			}
		}

		return false;
	}

	void InOrder()
	{
		_InOrder(_root);
		cout << endl;
	}

	bool FindR(const K& key)
	{
		return _FindR(_root, key);
	}

	bool InsertR(const K& key)
	{
		return _InsertR(_root, key);
	}

	bool EraseR(const K& key)
	{
		return _EraseR(_root, key);
	}

private:
	bool _EraseR(Node*& root, const K& key)
	{
		if (root == nullptr)
			return false;

		if (root->_key < key)
		{
			return _EraseR(root->_right, key);
		}
		else if (root->_key > key)
		{
			return _EraseR(root->_left, key);
		}
		else
		{
			// 删除
			if (root->_left == nullptr)
			{
				Node* del = root;
				root = root->_right;
				delete del;

				return true;

			}
			else if (root->_right == nullptr)
			{
				Node* del = root;
				root = root->_left;
				delete del;

				return true;
			}
			else
			{
				Node* subLeft = root->_right;
				while (subLeft->_left)
				{
					subLeft = subLeft->_left;
				}

				swap(root->_key, subLeft->_key);

				// 转换成在子树去递归删除
				return _EraseR(root->_right, key);
			}
		}
	}

	bool _InsertR(Node*& root, const K& key)
	{
		if (root == nullptr)
		{
			root = new Node(key);
			return true;
		}

		if (root->_key < key)
			return _InsertR(root->_right, key);
		else if (root->_key > key)
			return _InsertR(root->_left, key);
		else
			return false;
	}

	bool _FindR(Node* root, const K& key)
	{
		if (root == nullptr)
		{
			return false;
		}

		if (root->_key < key)
		{
			return _FindR(root->_right, key);
		}
		else if (root->_key > key)
		{
			return _FindR(root->_left, key);
		}
		else
		{
			return true;
		}
	}

	void _InOrder(Node* root)
	{
		if (root == nullptr)
			return;

		_InOrder(root->_left);
		cout << root->_key << " ";
		_InOrder(root->_right);
	}
private:
	Node* _root = nullptr;
};

// 改造二叉搜索树为KV结构
template<class K, class V>
struct BSTNode
{
	BSTNode(const K& key = K(), const V& value = V())
		: _pLeft(nullptr), _pRight(nullptr), _key(key), _Value(value)
	{}
	BSTNode<T>* _pLeft;
	BSTNode<T>* _pRight;
	K _key;
	V _value
};

template<class K, class V>
class BSTree
{
	typedef BSTNode<K, V> Node;
	typedef Node* PNode;
public:
	BSTree() : _pRoot(nullptr) {}
	PNode Find(const K& key);

	bool Insert(const K& key, const V& value)
		bool Erase(const K& key)

private:
	PNode _pRoot;
};

void TestBSTree3()
{
	// 输入单词，查找单词对应的中文翻译
	BSTree<string, string> dict;
	dict.Insert("string", "字符串");
	dict.Insert("tree", "树");
	dict.Insert("left", "左边、剩余");
	dict.Insert("right", "右边");
	dict.Insert("sort", "排序");

	// 插入词库中所有单词
	string str;
	while (cin >> str)
	{
		BSTreeNode<string, string>* ret = dict.Find(str);
		if (ret == nullptr)
		{
			cout << "单词拼写错误，词库中没有这个单词:" << str << endl;
		}
		else
		{
			cout << str << "中文翻译:" << ret->_value << endl;
		}
	}
}

void TestBSTree4()
{
	// 统计水果出现的次数
	string arr[] = { "苹果", "西瓜", "苹果", "西瓜", "苹果", "苹果", "西瓜",
   "苹果", "香蕉", "苹果", "香蕉" };
	BSTree<string, int> countTree;

	for (const auto& str : arr)
	{
		// 先查找水果在不在搜索树中
		// 1、不在，说明水果第一次出现，则插入<水果, 1>
		// 2、在，则查找到的节点中水果对应的次数++
		//BSTreeNode<string, int>* ret = countTree.Find(str);
		auto ret = countTree.Find(str);
		if (ret == NULL)
		{
			countTree.Insert(str, 1);
		}
		else
		{
			ret->_value++;
		}
	}

	countTree.InOrder();
}