二叉树前序、中序、后序，递归和非递归算法

前两天在CoolShell上面看到todd的文章《二叉树迭代器算法》，很有收获，顺便试着写出了下面的代码

#include <iostream>
#include <stack>

using std::cout;
using std::endl;
using std::stack;

struct Node
{
	int val;
	Node* left;
	Node* right;

	Node() {left = NULL;right = NULL;}
};

//中序递归
void Inorder_traverse(Node *node)
{
	if (NULL != node)
	{
		Inorder_traverse(node->left);
		cout << node->val << " ";
		Inorder_traverse(node->right);
	}
}
//中序非递归
void Inorder_traverse_nonDG(Node* node)
{
	stack<Node*> stk;
	do 
	{
		while(NULL != node)
		{
			stk.push(node);
			node = node->left;
		}

		do 
		{
			Node* top = stk.top();
			stk.pop();
			cout << top->val << " ";
			if (NULL != top->right)
			{
				node = top->right;
				stk.push(node);
				node = node->left;
				break;
			}
		} while (!stk.empty());
	} while (!stk.empty());
}
//前序递归
void Preorder_traverse(Node* node) 
{
	if (NULL != node)
	{
		cout << node->val << " ";
		Preorder_traverse(node->left);
		Preorder_traverse(node->right);
	}
}
//前序非递归
void Preorder_traverse_nonDG(Node* node)
{
	stack<Node*> stk;
	do 
	{
		while(NULL != node)
		{
			cout << node->val << " "; //do something
			if (NULL != node->right)
			{
				stk.push(node->right);
			}
			node = node->left;
		}

		node = stk.top();
		stk.pop();
		if (NULL != node->right)
		{
			stk.push(node->right);
		}
	} while (!stk.empty());
}
//后序递归
void Postorder_traverse(Node* node) 
{
	if (NULL != node)
	{
		Postorder_traverse(node->left);
		Postorder_traverse(node->right);
		cout << node->val << " ";
	}
}
//后序非递归
void Postorder_traverse_nonDG(Node* node)
{
	stack<Node*> stk;

	do 
	{
		while (NULL != node)
		{
			stk.push(node);
			node = node->left;
		}

		Node* tmp = NULL; //保存右子树根节点，判断右子树是否遍历

		do 
		{
			Node* top = stk.top();
			
			if (NULL != top->right && top->right != tmp)
			{
				node = top->right;
				break;
			}
			else
			{
				cout << top->val << " ";
				tmp = stk.top();
				stk.pop();
			}			
		} while (!stk.empty());
	} while (!stk.empty());
}

int main(int argc, char* argv[])
{
	//构造一颗树，丑陋的构造方法，只是为了简单测试一下
	/*Node* root = new Node;
	root->val = 4;
	
	Node* left = new Node;
	left->val = 2;
	root->left = left;
	left->left = new Node;
	left->left->val = 1;
	left->right = new Node;
	left->right->val = 3;

	Node* right = new Node;
	right->val = 6;
	root->right = right;
	right->left = new Node;
	right->left->val = 5;
	right->right = new Node;
	right->right->val = 7;*/

	Node* root = new Node;
	root->val = 4;
	
	Node* left = new Node;
	left->val = 2;
	root->left = left;
	left->left = new Node;
	left->left->val = 1;
	left->right = new Node;
	left->right->val = 3;

	Node* left1 = left->left;

	Node* left2 = new Node;
	left2->val = 2;
	left1->left = left2;
	left2->left = new Node;
	left2->left->val = 1;
	left2->right = new Node;
	left2->right->val = 3;

	Node* right = new Node;
	right->val = 6;
	root->right = right;
	right->left = new Node;
	right->left->val = 5;
	right->right = new Node;
	right->right->val = 7;

	cout << "Inorder traverse: ";
	Inorder_traverse(root);
	cout << endl;

	cout << "Inorder traverse without DG: ";
	Inorder_traverse_nonDG(root);
	cout << endl;

	cout << "Preorder traverse: ";
	Preorder_traverse(root);
	cout << endl;

	cout << "Preorder traverse without DG: ";
	Preorder_traverse_nonDG(root);
	cout << endl;

	cout << "Postorder traverse: ";
	Postorder_traverse(root);
	cout << endl;

	cout << "Postorder traverse without DG: ";
	Postorder_traverse_nonDG(root);
	cout << endl;
}