本贴给出二叉树先序、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，直接用于考研答题。
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
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