最近在看關於樹結構方面的東西，想著實現二叉樹的遍歷操作。層序，先序，中序都還好，後序就比較麻煩，下面的地址很好的解釋了遞迴與非遞迴的實現方法，在此給出另一種非遞迴實現後序遍歷二叉樹的方法，通過複雜化資料結構，使得演算法更簡單。

http://blog.csdn.net/pi9nc/article/details/13008511

#include"iostream"
#include "stack"
using namespace std;
#define N 7

typedef struct node
{
	struct node* leftchild;
	struct node* rightchild;
	struct node* parent;
	int data;
	int flag;
}BiTreeNode, *bt;

BiTreeNode* CreateNode(int data)
{
	BiTreeNode* t=new BiTreeNode;
	t->data=data;
	t->leftchild=NULL;
	t->rightchild=NULL;
	t->flag=0;
	return t;
}

bt CreateBiTree()
{
	bt p[N]={NULL};
	for(int i=0;i<N;i++)
	{
		p[i]=CreateNode(i+1);
	}
	for(int i=0;i<N/2;i++)
	{
		p[i]->leftchild=p[2*i+1];
		p[i]->rightchild=p[2*i+2];
	}

	for(int i=0;i<N;i++)
	{
		if(i==0)
			p[i]->parent=NULL;
		else if(i%2==0)
			p[i]->parent=p[i/2-1];
		else
			p[i]->parent=p[(i+1-1)/2];
	}
	return p[0];
}

int max(int a,int b)
{
	return a>b?a:b;
}
int depth(bt t)
{
	if(t==NULL)return 0;
	int nLeftDepth=depth(t->leftchild);
	int nRightDepth=depth(t->rightchild);

	return 1+max(nLeftDepth,nRightDepth);
	
}
//層序遍歷
void PrintNodeByOrder(bt b,int level)
{
	if(b==NULL || level<1)
		return;
	if(1 == level)
	{
		cout<<b->data<<"  ";
		return;
	}
	PrintNodeByOrder(b->leftchild,level-1);
	PrintNodeByOrder(b->rightchild,level-1);
}
void LevelTraverse(bt b)
{
	int nHeight=depth(b);
	if(nHeight==0)
		cout<<"樹為空"<<endl;
	for(int i=1;i<=nHeight;i++)
	{
		PrintNodeByOrder(b,i);
		cout<<endl;
	}
}

//先序非遞迴遍歷
void PreTraverse(bt t)
{
	stack<bt>c;
	bt q=t;
	while(q!=NULL || !c.empty())
	{
		while(q!=NULL)
		{
			cout<<q->data;
			c.push(q);
			q=q->leftchild;
		}
		if(!c.empty())
		{
			q=c.top();
			c.pop();
			q=q->rightchild;
		}
	}
}

//中序非遞迴遍歷
void InTraverse(bt t)
{
	stack<bt>c;
	bt q=t;
	while(q!=NULL || !c.empty())
	{
		while(q!=NULL)
		{
			c.push(q);
			q=q->leftchild;
			
		}
		
		if(!c.empty())
		{
			q=c.top();
			cout<<q->data;
			c.pop();
			q=q->rightchild;
		}
	}
}

//後序非遞迴遍歷
void PostOrder(bt t)
{
	bt m=t;
	while(m!=NULL)
	{
		switch(m->flag)
		{
			case 0:
				{
					m->flag=1;
					if(m->leftchild!=NULL)
						m=m->leftchild;
					break;
				}
			case 1:
				{
					m->flag=2;
					if(m->rightchild!=NULL)
						m=m->rightchild;
					break;
				}
			case 2:
				{
					m->flag=0;
					cout<<m->data;
					m=m->parent;
					break;
				}
		}
	}
}
int main()
{
	BiTreeNode* p=CreateBiTree();

	cout<<"層次遍歷"<<endl;
	LevelTraverse(p);
	cout<<endl;

	cout<<"先序非遞迴遍歷"<<endl;
	PreTraverse(p);
	cout<<endl;

	cout<<"中序非遞迴遍歷"<<endl;
	InTraverse(p);
	cout<<endl;

	cout<<"後序非遞迴遍歷"<<endl;
	PostOrder(p);
	cout<<endl;
	return 0;
}