【C++】搜索二叉树实现

局部变量和传引用问题

#pragma once

namespace xiong
{

	template<class K, class V>
	struct TreeNode
	{

		K _key;
		V _val;
		TreeNode<K, V>* _left;
		TreeNode<K, V>* _right;

		TreeNode(const K& key, const V& val)
			:_key(key)
			,_val(val)
			,_left(nullptr)
			,_right(nullptr)
		{}
	};

	template<class K, class V>
	class BSTree
	{
		typedef TreeNode<K, V> Node;
	public:
		bool Insert(const K& key, const V& val)
		{
			Node* node = new Node(key, val);

			if (_root == nullptr)
			{
				_root = node;
				return true;
			}
			
			Node* cur = _root;
			Node* prev = nullptr;
			while (cur)
			{
				prev = cur;
				if (key < cur->_key)
				{
					cur = cur->_left;
				}
				else if (key > cur->_key)
				{
					cur = cur->_right;
				}
				else
					return false;
			}
			//因为cur这里时局部变量，无法直接修改，所以要判断上一结点指向
			//链接，区分左右结点
			if (key < prev->_key)
				prev->_left = node;
			if (key > prev->_key)
				prev->_right = node;
			return true;
		}

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

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

		//删除结点
		bool Erase(const K& key)
		{
			if (!Find(key))
				return false;
			Node* cur = _root;
			Node* prev = nullptr;

			while (cur)
			{
				
				if (key < cur->_key)
				{
					prev = cur;
					cur = cur->_left;
				}
				else if (key > cur->_key)
				{
					prev = cur;	
					cur = cur->_right;
				}
				else
				{
					//删除结点左为空
					if (cur->_left == nullptr)
					{
						//结点为树的根结点
						if (cur == _root)
						{
							_root = cur->_right;
							
						}
						else
						{
							//链接
							if (prev->_right == cur)
							{
								prev->_right = cur->_right;
							}
							else
							{
								prev->_left = cur->_right;
							}
						}
						delete cur;

					}
					//删除结点右为空
					else if (cur->_right == nullptr)
					{
						//结点为树的根结点
						if (cur == _root)
						{
							_root = cur->_left;
						}
						else
						{
							//链接
							if (prev->_right == cur)
							{
								prev->_right = cur->_left;
							}
							else
							{
								prev->_left = cur->_left;
							}
						}
						delete cur;
					}
					//删除结点左右均不为空
					else
					{
						//找左子树最大结点，替换要删除的结点
						Node* leftmax = cur->_left;
						prev = cur;
						while (leftmax->_right)
						{
							prev = leftmax;
							leftmax = leftmax->_right;
						}
						cur->_key = leftmax->_key;

						//链接
						if (prev->_left == leftmax)
						{
							prev->_left = leftmax->_left;
						}
						if (prev->_right == leftmax)
						{
							prev->_right = leftmax->_left;
						}
						delete leftmax;
					}
					return true;
				}
			}
			return false;
		}

		//中序遍历
		void Inorder()
		{
			_Inorder(_root);
			cout << endl;
		}

		//递归插入
		bool InsertR(const K& key)
		{
			return _InsertR(_root, key);
		}

		//递归删除
		bool EraseR(const K& key)
		{
			return _EraseR(_root, key);
		}

		//递归查找
		bool FindR(const K& key)
		{
			return _FindR(_root, key);
		}

	private:
		
		bool _InsertR(Node*& root, const K& key)
		{
			if (root == nullptr)
			{
				//因为这里加了一层_InsertR 函数，为传引用传参，
				//故可以直接修改root不用判断左右
				root = new Node(key);
				return true;
			}
			if (key < root->_key)
				return _InsertR(root->_left, key);	
			else if (key > root->_key)
				return _InsertR(root->_right, key);
			else
				return false;
		}

		bool _EraseR(Node*& root, const K& key)
		{

			if (root == nullptr)
				return false;
			if (key < root->_key)
				return _EraseR(root->_left, key);
			else if (key > root->_key)
				return _EraseR(root->_right, key);
			else
			{
				if (root->_left == nullptr)
				{
					root = root->_right;
				}
				else if (root->_right == nullptr)
				{
					root = root->_left;
				}
				else
				{
					Node* leftmax = root->_left;
					while (leftmax->_right)
					{
						leftmax = leftmax->_right;
					}
					swap(root->_key, leftmax->_key);
					//这里的leftmax是临时变量，如果直接传leftmax
					//修改递归内的root没有实际效果，所以只能传root->left
					//return _EraseR(leftmax, key);
					return _EraseR(root->_left, key);

				}
				return true;
			}
		}

		bool _FindR(Node*& root, const K& key)
		{
			if (root == nullptr)
				return false;
			if (root->_key == key)
			{
				return true;
			}
			return _FindR(root->_left, key) || _FindR(root->_right, key);
		}

		void _Inorder(Node* root)
		{
			if (root == nullptr)
				return;
			_Inorder(root->_left);
			cout << root->_key << ":" << root->_val << endl;
			_Inorder(root->_right);
			return;
		}


		Node* _root = nullptr;
	};

}