数据结构练习（39）二叉树前中后序遍历的非递归实现

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

struct TreeNode {
int m_value;
TreeNode* m_lhs;
TreeNode* m_rhs;
};

void PreOrderVisit_1(TreeNode* root)
{
stack<TreeNode*> s;
TreeNode* pNode = root;

while (pNode || !s.empty())
{
while (pNode)
{
s.push(pNode);
cout << pNode->m_value << " ";
pNode = pNode->m_lhs;
}
if (!s.empty())
{
pNode = s.top();
s.pop();
pNode = pNode->m_rhs;
}
}
}

void PreOrderVisit_2(TreeNode* root)
{
if (root == NULL)
return ;

stack<TreeNode*> s;
s.push(root);

while (!s.empty())
{
TreeNode* pNode = s.top();
s.pop();
cout << pNode->m_value << " ";

if (pNode->m_rhs)
s.push(pNode->m_rhs);
if (pNode->m_lhs)
s.push(pNode->m_lhs);
}
}

void InOrderVisit(TreeNode* root)
{
stack<TreeNode*> s;
TreeNode* pNode = root;

while (pNode || !s.empty())
{
while (pNode)
{
s.push(pNode);
pNode = pNode->m_lhs;
}
if (!s.empty())
{
pNode = s.top();
s.pop();
cout << pNode->m_value << " ";
pNode = pNode->m_rhs;
}
}
}

void PostOrderVisit(TreeNode* root)
{
if (root == NULL)
return ;

stack<TreeNode*> s;
s.push(root);
TreeNode* preNode = NULL;

while (!s.empty())
{
TreeNode* curNode = s.top();
TreeNode* lastNode = curNode->m_rhs;

if (lastNode == NULL)
lastNode = curNode->m_lhs;

if (lastNode == NULL || lastNode == preNode)
{
cout << curNode->m_value << " ";
preNode = curNode;
s.pop();
}
else if (curNode->m_lhs == NULL || curNode->m_lhs == preNode)
{
s.push(curNode->m_rhs);
}
else
s.push(curNode->m_lhs);
}
}

enum _travel_type {
visit, travel
};

typedef pair<enum _travel_type, TreeNode*> NodePair;

void InOrderVisit_2(TreeNode* root)
{
if (root == NULL)
return;

stack<NodePair> s;
s.push(NodePair(travel, root));

while (!s.empty())
{
NodePair np = s.top();
s.pop();

TreeNode* pNode = np.second;

if (np.first == visit)
cout << pNode->m_value << " ";
else
{
if (pNode->m_rhs)
s.push(NodePair(travel, pNode->m_rhs));

s.push(NodePair(visit, pNode));

if (pNode->m_lhs)
s.push(NodePair(travel, pNode->m_lhs));
}
}
}

void PostOrderVisit_2(TreeNode* root)
{
if (root == NULL)
return ;

stack<NodePair> s;
s.push(NodePair(travel, root));

while (!s.empty())
{
NodePair np = s.top();
s.pop();
TreeNode* pNode = np.second;

if (np.first == visit)
cout << pNode->m_value << " ";
else
{
s.push(NodePair(visit, pNode));
if (pNode->m_rhs)
s.push(NodePair(travel, pNode->m_rhs));
if (pNode->m_lhs)
s.push(NodePair(travel, pNode->m_lhs));
}
}
}