二叉树的遍历

typedef struct BiTree* Node;
typedef struct BiTree* Tree;
struct BiTree
{
	int Element;
	Node Left;
	Node Right;
	bool isFirst;   //从下向上出栈过程中,第一次出现在栈顶
};


//先序遍历, 递归
void TraverseTreePreOrder(Tree T)
{
	if(T != NULL)
	{
		cout<<T->Element<<" ";
		TraverseTreePreOrder(T->Left);
		TraverseTreePreOrder(T->Right);
	}
}

//中序遍历, 递归
void TraverseTreeInOrder(Tree T)
{
	if(T != NULL)
	{
		TraverseTreeInOrder(T->Left);
		cout<<T->Element<<" ";
		TraverseTreeInOrder(T->Right);
	}
}

//后序遍历,递归
void TraverseTreePostOrder(Tree T)
{
	if(T != NULL)
	{
		TraverseTreePostOrder(T->Left);
		TraverseTreePostOrder(T->Right);
		cout<<T->Element<<" ";
	}
}

//先序遍历. 非递归
void TraverseTreePreOrder2(Tree T)
{
	stack<Node> Stack;
	while(T!= NULL || !Stack.empty())   //每进行一次while,都是从左儿子到右儿子
	{
		while(T != NULL)   //一直遍历最左边的节点
		{
			cout<<T->Element<<" ";
			Stack.push(T);
			T = T->Left;
		}
		//如果遍历到底了,就向上一层, 遍历右儿子
		T =Stack.top(); 
		T = T->Right;  
		Stack.pop();  
   
	}
}

//中序遍历, 非递归
void TraverseTreeInOrder2(Tree T)
{
	stack<Node> Stack;
	while(T!= NULL || !Stack.empty())
	{
		while(T != NULL)
		{
			Stack.push(T);	
			T = T->Left;
		}
		T = Stack.top;
		Stack.pop();
		cout<<T->Element<<" ";
		T = T->Right;
	}
}

//后序遍历, 非递归
void TraverseTreePostOrder(Tree T)
{
	stack<Node> Stack;
	while(T != NULL || !Stack.empty())
	{
		while(T != NULL)
		{
			Stack.push(T);
			T->isFirst = true; //所有节点在初始入栈时都会在此被设为true.
			T = T->Left;
		}
		T = Stack.top();
		//Stack.pop();
		if(T->isFirst)  //左节点被遍历完,准备向右节点遍历时
		{
			T->isFirst = false;
			//Stack.push(T);
			T = T->Right;
		}
		else  //右节点被遍历完,又回到这个节点,准备走向父节点
		{
			Stack.pop();
			cout<<T->Element<<" ";
			T = NULL:
		}

	}
}