法一：实现思路：一个栈 先按 根->右子树->左子树的顺序访问二叉树。访问时不输出。另一个栈存入前一个栈只进栈的结点。
最后输出后一个栈的结点数据。
#include<stdio.h>
#include<stdlib.h>
typedef struct TreeNode{
char element;
struct TreeNode *left,*right;
}Tree,*BTree;
typedef struct StackNode{
BTree data;
struct StackNode *next;
}Stack,*PStack;
typedef struct{
PStack top;
}LinkStack,*PLinkStack;
//初始化空栈
PLinkStack Init_Stack(void){
PLinkStack S;
S=(PLinkStack)malloc(sizeof(LinkStack));
if(S){
S->top=NULL;
}
return S;
}
//压栈
void Push_Stack(PLinkStack S,BTree T){
PStack p;
p=(PStack)malloc(sizeof(Stack));
p->data=T;
p->next=S->top;
S->top=p;
}
//判空
int empty_Stack(PLinkStack S){
if(S->top){
return 0;
}else{
return 1;
}
}
//出栈
PStack Pop_Stack(PLinkStack S){
PStack q;
if(empty_Stack(S)){
return S->top;
}else{
q=S->top;
S->top=S->top->next;
}
return q;
}
//销毁栈
void DestroyStack(PLinkStack S){
PStack del;
while(S->top!=NULL){
del=S->top;
S->top=S->top->next;
free(del);
}
free(S);
}
BTree BuildTree(void){
char ch;
BTree node;
ch=getchar();
if(ch=='#'){
node=NULL;
}else{
node=(BTree)malloc(sizeof(Tree));
node->element=ch;
node->left=BuildTree();
node->right=BuildTree();
}
return node;
}
void NotRecursionPostOrder(BTree T){
PLinkStack S,CS;
S=Init_Stack();
CS=Init_Stack();
while(T || !empty_Stack(S)){
if(T){
Push_Stack(S,T);
Push_Stack(CS,T);
T=T->right;
}else{
T=Pop_Stack(S)->data;
T=T->left;
}
}
while(CS->top!=NULL){
printf("%c",CS->top->data->element);
CS->top=CS->top->next;
}
DestroyStack(CS);
}
int main(void){
BTree T;
T=BuildTree();
NotRecursionPostOrder(T);
return 0;
}
法二：实现思路。按先序遍历访问每一个结点。存入栈中，当为空时，就出立即栈（第一次出栈）。出栈后应该立即进栈，去访问进栈结点的右结点，这样可以保证先输出左、右结点，再输出根结点。二次进栈利用flag标记。
#include<stdio.h>
#include<stdlib.h>
typedef struct TreeNode {
char element;
int flag;
struct TreeNode *left, *right;
}Tree, *BTree;
typedef struct StackNode {
BTree data;
struct StackNode *next;
}Stack, *PStack;
typedef struct {
PStack top;
}LinkStack, *PLinkStack;
//初始化空栈
PLinkStack Init_Stack(void) {
PLinkStack S = (PLinkStack)malloc(sizeof(LinkStack));
if (S) {
S->top = NULL;
}
return S;
}
//压栈
void Push_Stack(PLinkStack S, BTree T) {
PStack p;
p = (PStack)malloc(sizeof(Stack));
p->data = T;
p->next = S->top;
S->top = p;
}
//判空
int empty_Stack(PLinkStack S) {
if (S->top) {
return 0;
}
else {
return 1;
}
}
//出栈
PStack Pop_Stack(PLinkStack S) {
PStack q = S->top;
S->top = S->top->next;
return q;
}
BTree BuildTree(void) {
BTree t;
char ch;
ch = getchar();
if (ch == '#') {
t = NULL;
}
else {
t = (BTree)malloc(sizeof(Tree));
t->element = ch;
t->left = BuildTree();
t->right = BuildTree();
}
return t;
}
void DestroyStack(PLinkStack S){
PStack p;
while(S->top){
p=S->top;
free(p);
S->top=S->top->next;
}
}
void NotRecursionPostOrder(BTree T) {
PLinkStack S;
S = Init_Stack();
while (T || !empty_Stack(S)) {
if (T) {
T->flag = 0;
Push_Stack(S, T);
T = T->left;
}
else {
T = Pop_Stack(S)->data;
if (T->flag == 0) {
T->flag = 1;
Push_Stack(S, T);
T = T->right;
}
else {
if (T->flag == 1) {
printf("%c", T->element);
T = NULL;
}
}
}
}
DestroyStack(S);//销毁栈
}
int main(void) {
BTree T;
T = BuildTree();
NotRecursionPostOrder(T);
return 0;
}
