C++ Binary Tree

This article mainly writes about the structure of the binary tree, the middle order, preorder, postorder, and layer order traversal algorithms.

The structure of the binary tree, this article uses the following binary tree to traverse:

Middle-order traversal: left child node ----> middle node ----> right child node

Preorder traversal: middle node----->left child node---->right child node

Post-order traversal: left child node----->right child node----->intermediate node

Sequence traversal: traverse layer by layer from top to bottom

Take the binary tree structure in the above figure as an example, and start writing the code:

#include <iostream>
#include <queue>
using namespace std;


template <class T> class BinaryTree;


template <class T>
class TreeNode
{
	template <class T>
	friend class BinaryTree;
public:

	TreeNode(const T & d):data(d)
	{
		leftChild = rightChild = NULL;
	}
//private:
	T data;
	TreeNode *leftChild;
	TreeNode *rightChild;

};

template <class T>
class BinaryTree
{
public:
	void InOrder(); //中序遍历    左->中->右
	void InOrder(TreeNode<T> * current);  
	void PreOrder(); //前序遍历  中->左->右
	void PreOrder(TreeNode<T> *current);
	void PostOrder();//后序遍历  左->右->中
	void PostOrder(TreeNode<T>*current);
	void LevelOrder(); //层序遍历
	void Visit(TreeNode<T>*current);

	int getTreeHight(TreeNode<T>* root);  //计算思路:树的深度=左链的深度和右链深度的最大值 +1

	TreeNode<T> *  getRoot()
	{
		return root;
	}

//private:
	TreeNode<T> *root;

};

template <class T>
void BinaryTree< T>::Visit(TreeNode<T>*current)
{
	if (current)
		cout << current->data << " ";
}
template <class T>
void BinaryTree< T>::InOrder(TreeNode<T>*current)
{
	if (current)
	{
		InOrder(current->leftChild);
		Visit(current);
		InOrder(current->rightChild);
	}
}
template <class T>
void BinaryTree< T>::InOrder()
{
	InOrder(root);
}
template <class T>
void BinaryTree<T>::PreOrder()
{
	PreOrder(root);
}
template <class T>
void BinaryTree<T>::PreOrder(TreeNode<T> *current)
{
	if (current)
	{
		Visit(current);
		PreOrder(current->leftChild);
		PreOrder(current->rightChild);
	}
}

template <class T>
void BinaryTree<T>::PostOrder()
{
	PostOrder(root);
}

template <class T>
void BinaryTree<T>::PostOrder(TreeNode<T> *current)
{
	if (current)
	{
		PostOrder(current->leftChild);
		PostOrder(current->rightChild);
		Visit(current);
	}
}

template <class T>
void BinaryTree<T>::LevelOrder()
{
	//层序遍历，充分利用了queue先进先出的特点
	queue<TreeNode<T>* > q;

	TreeNode<T>* current = root;

	while (current)
	{
		Visit(current);
		if (current->leftChild) q.push(current->leftChild); //先把左子节点放到队列
		if (current->rightChild) q.push(current->rightChild); //再把右子节点放到队列

		if (q.empty()) return;  //到队列空的时候就返回

		current = q.front(); //当前指针指向先放进去的指针
		q.pop();  //将上边这个弹出队列
	}
}

template <class T>
int BinaryTree<T>::getTreeHight(TreeNode<T>* root) 
{
	if (NULL == root)
		return 0;

	int leftHigh = getTreeHight(root->leftChild);
	int rightHigh = getTreeHight(root->rightChild);

	int maxHigh = leftHigh >= rightHigh ? leftHigh + 1 : rightHigh + 1;

	return maxHigh;

}

int main()
{
	TreeNode<char> node1('+'),node2('-'), node3('*'), node4('/'), node5('A'), node6('B'), node7('C'), node8('D'), node9('E');

	BinaryTree<char> tree;
	

	tree.root = &node1;

	node1.leftChild = &node2;
	node1.rightChild = &node9;

	node2.leftChild = &node3;
	node2.rightChild = &node8;

	node3.leftChild = &node4;
	node3.rightChild = &node7;

	node4.leftChild = &node5;
	node4.rightChild = &node6;

	//中序遍历
	cout << "中序遍历:   ";
	tree.InOrder();
	cout << endl;

	//前序遍历
	cout << "前序遍历:   ";
	tree.PreOrder();
	cout << endl;

	//后序遍历
	cout << "后序遍历:  ";
	tree.PostOrder();
	cout << endl;

	//层序遍历
	cout << "层序遍历  ";
	tree.LevelOrder();
	cout << endl;


	cout << "树的深度 ";
	cout << tree.getTreeHight(tree.getRoot())<<endl;

	return 0;
}

operation result: