【数据结构】中序线索化二叉树后实现一个迭代器来遍历二叉树

1.创建二叉树的结点

#pragma once
#include<iostream>
#include<stack>
using namespace std;
enum PointerTag
{
	THREND,
	LINK,
};
template<class T>
struct BinaryTreeThdNode
{
	typedef BinaryTreeThdNode<T> Node;
	BinaryTreeThdNode(T data)
		:_data(data), _left(NULL), _right(NULL),_father(NULL), _leftTag(LINK), _rightTag(LINK)
	{}
	T _data;
	Node* _left;
	Node* _right;
	Node* _father;     //为后续线索化的遍历设置的父指针，此处可以忽略
	PointerTag _leftTag;
	PointerTag _rightTag;
};

2.创建二叉树

template<class T>
class BinaryTreeThd
{
public:
	typedef BinaryTreeThdNode<T> Node;
	typedef TreeIterator<T, T*, T&> Iterator;
	BinaryTreeThd()
	{}
	BinaryTreeThd(T* arr, size_t size, T invalid)   //非递归创建树

	{
		stack<Node*> s;
		size_t index = 0;
		Node* cur = NULL;
		while (index < size)
		{
			while (index < size && (arr[index] != invalid))
			{
				if (index == 0)   //根节点特殊处理
				{
					cur = new Node(arr[index++]);
					_root = cur;
				}
				else
				{
					cur->_left = new Node(arr[index++]);   //创建左结点
					Node* tmp = cur;
					cur = cur->_left;
					cur->_father = tmp;
				}
				s.push(cur);
			}
			index++;
			Node* top = s.top();
			s.pop();
			if ((index<size)&&(arr[index] != invalid))
			{
				cur = top;
				cur->_right = new Node(arr[index++]);   //创建右节点
				Node* tmp = cur;
				cur = cur->_right;
				cur->_father = tmp;
				s.push(cur);
			}
		}
	}
private:
    Node* _root;
}

/*******************中序线索化递归实现********************/
	void InorderThreading()
	{
		Node* prev = NULL;
		_InorderThreading(_root, prev);
	}
	void _InorderThreading(Node* cur,Node*& prev)
	{
		if (cur == NULL)
			return;
		_InorderThreading(cur->_left, prev);        //递归线索化左子树
		if (cur->_left == NULL)
		{
			cur->_leftTag = THREND;
			cur->_left = prev;
		}
		if (prev && (prev->_right == NULL))
		{
			prev->_rightTag = THREND;
			prev->_right = cur;
		}
		prev = cur;
		_InorderThreading(cur->_right, prev);   //递归线索化右子树

		
	}

/**************中序线索化非递归实现**********************/
void InorderThreading()
	{
		Node* cur = _root;
		Node* prev = NULL;
		stack<Node*> s;
		while (cur || !s.empty())
		{
			while (cur)
			{
				s.push(cur);
				cur = cur->_left;
			}
			Node* top = s.top();
		
			if ((top->_left == NULL))
			{
				top->_left = prev;
				top->_leftTag = THREND;
			}
			
			if (prev&&(prev->_right == NULL))
			{
				prev->_rightTag = THREND;
				prev->_right = top;
			}
			prev = top;
			if (top->_right != NULL)
				cur = top->_right;
			s.pop();
			
		}
	}

3.迭代器部分

template<class T,class Ptr,class Ref>
class TreeIterator
{
public: 
	typedef TreeIterator<T, Ptr, Ref> self;
	typedef TreeIterator<T, T*, T&> Iterator;
	typedef BinaryTreeThdNode<T> Node;
	TreeIterator(Node* p)
		:ptr(p)
	{}
	TreeIterator()
	{}
	self& operator++()
	{
		if (ptr->_rightTag == THREND)
		{
			ptr = ptr->_right;
		}
		else if (ptr->_rightTag == LINK)
		{
			Node* tmp = ptr->_right;
			while (tmp&&tmp->_leftTag == LINK)
			{
				tmp = tmp->_left;
			}
			ptr = tmp;
		}
		return *this;
	}
	bool operator!=(Iterator it)
	{
		return !(ptr == it.ptr);
	}
	Ref operator*()
	{
		return ptr->_data;
	}
private:
	Node* ptr;
};

Iterator Begin()
	{
		Node* cur = _root;
		while (cur->_leftTag)
			cur = cur->_left;
		return Iterator(cur);
	}
	Iterator End()
	{
		Node* cur = _root;
		while (cur!=NULL)
		{
			cur = cur->_right;
		}
		return Iterator(cur);
	}

4.测试

void TestInOrderIter()
{
	int array[10] = { 1, 2, 3, '#', '#', 4, '#', '#', 5, 6 };
	int array1[15] = { 1, 2, '#', 3, '#', '#', 4, 5, '#', 6, '#', 7, '#', '#', 8 };
	BinaryTreeThd<int> bt(array, 10, '#');
	bt.InorderThreading();
	BinaryTreeThd<int>::Iterator it;
	for (it = bt.Begin(); it != bt.End();++it)
	{
		cout << *it << " ";
	}
	cout << endl;
	BinaryTreeThd<int>bt1(array1, 15, '#');
	bt1.InorderThreading();
	BinaryTreeThd<int>::Iterator it1;
	for (it1 = bt1.Begin(); it1 != bt1.End(); ++it1)
	{
		cout << *it1 << " ";
	}
	cout << endl;
}