二叉树先序、中序、后序三种遍历的非递归算法

二叉树先序、中序、后序三种遍历的非递归算法，此三个算法可视为标准算法。

1.先序遍历非递归算法

#define maxsize 100

typedef struct

{

Bitree Elem[maxsize];

int top;

}SqStack;

void PreOrderUnrec(Bitree t)

{

SqStack s;

StackInit(s);

p=t;

while (p!=null || !StackEmpty(s))

{

while (p!=null) //遍历左子树

{

visite(p->data);

push(s,p);

p=p->lchild;

}//endwhile

if (!StackEmpty(s)) //通过下一次循环中的内嵌while实现右子树遍历

{

p=pop(s);

p=p->rchild;

}//endif

}//endwhile

}//PreOrderUnrec

2.中序遍历非递归算法

#define maxsize 100

typedef struct

{

Bitree Elem[maxsize];

int top;

}SqStack;

void InOrderUnrec(Bitree t)

{

SqStack s;

StackInit(s);

p=t;

while (p!=null || !StackEmpty(s))

{

while (p!=null) //遍历左子树

{

push(s,p);

p=p->lchild;

}//endwhile

if (!StackEmpty(s))

{

p=pop(s);

visite(p->data); //访问根结点

p=p->rchild; //通过下一次循环实现右子树遍历

}//endif

}//endwhile

}//InOrderUnrec

3.后序遍历非递归算法

#define maxsize 100

typedef enum{L,R} tagtype;

typedef struct

{

Bitree ptr;

tagtype tag;

}stacknode;

typedef struct

{

stacknode Elem[maxsize];

int top;

}SqStack;

void PostOrderUnrec(Bitree t)

{

SqStack s;

stacknode x;

StackInit(s);

p=t;

do

{

while (p!=null) //遍历左子树

{

x.ptr = p;

x.tag = L; //标记为左子树

push(s,x);

p=p->lchild;

}

while (!StackEmpty(s) && s.Elem[s.top].tag==R)

{

x = pop(s);

p = x.ptr;

visite(p->data); //tag为R，表示右子树访问完毕，故访问根结点

}

if (!StackEmpty(s))

{

s.Elem[s.top].tag =R; //遍历右子树

p=s.Elem[s.top].ptr->rchild;

}

}while (!StackEmpty(s));

}//PostOrderUnrec