非递归实现树的遍历

【代码】

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

typedef struct Node{
	char key;
	struct Node *lchild, *rchild;
}*Tree, TNode;

void PreOrder(Tree T) //先序遍历
{
	if (T == NULL)
		return;
	TNode *curr = T;
	//TNode *tmp;
	stack<Tree> s;
	while (curr != NULL || !s.empty()) {
		if (curr != NULL) {
			cout<<curr->key;
			s.push(curr);
			curr = curr->lchild;
		}
		else {
			curr = s.top();
			s.pop();
			curr = curr->rchild;
		}
	}
	/*
	while (curr != NULL) {
		cout<<curr->key;
		s.push(curr);
		curr = curr->lchild;
	}
	while(!s.empty()) {
		curr = s.top();
		s.pop();
		tmp = curr->rchild;
		while(tmp != NULL) {
			cout<<tmp->key;
			s.push(tmp);
			tmp = tmp->lchild;
		}
	}
	*/
}

void InOrder(Tree T)  //中序遍历
{
	if (T == NULL)
		return;
	TNode *curr = T;
	//TNode *tmp;
	stack<Tree> s;
	while ((curr != NULL) || !s.empty()) {
		if (curr != NULL) {
			s.push(curr);
			curr = curr->lchild;
		}
		else {
			curr = s.top();
			cout<<curr->key;
			s.pop();
			curr = curr->rchild;
		}
	}

}

void PostOrder(Tree T) //后序遍历
{
	if (T == NULL)
		return ;
	TNode *curr = T, *pre = NULL;
	stack<Tree> s;
	while (curr != NULL || !s.empty()) {
		if (curr != NULL) {
			s.push(curr);
			curr = curr->lchild;
		}
		else {
			curr = s.top();
			s.pop();
			if (curr->rchild != NULL && curr->rchild != pre) {
				s.push(curr);
				curr = curr->rchild;
			}
			else {
				cout<<curr->key;
				pre = curr;
				curr = NULL;
			}
		}
	}
}

Tree createTree(char *s, int n, int i) //建树
{
	if (i >= n)
		return NULL;
	TNode *curr;
	curr = (TNode *)malloc(sizeof(TNode));
	curr->key = s[i];

	curr->lchild = createTree(s, n, 2*(i+1)-1);
	curr->rchild = createTree(s, n, 2*(i+1));
	return curr;
}

void freeTree(Tree T)  //释放
{
	if (T != NULL){
		freeTree(T->lchild);
		freeTree(T->rchild);
		delete T;
	}
}

int main(void)
{
	char s[] = "ABCDEFG";
	Tree T;
	T = createTree(s, 7, 0);
	InOrder(T);
	cout<<endl;
	PreOrder(T);
	cout<<endl;
	PostOrder(T);
	cout<<endl;
	freeTree(T);
	return 0;
}