二叉树后序遍历迭代器（仅支持++）

数据结构作业，昨天康大佬（）优化了一下觉得不错，贴上来，供测试使用

#include <iostream>#include <stack>using namespace std;template <class Type> struct BTNode {    BTNode *left;    Type data;    BTNode *right;    BTNode(Type x) {        data = x;        left = right = NULL;    }};template <class Type> class PostOrder;template <class Type> class BinaryTree {private:    BTNode<Type> *root;    friend class PostOrder<Type>;public:    BinaryTree(BTNode<Type>*t) { root = t; }};//Base class for BT Iteratortemplate <class Type> class TreeIterator {protected:    const BinaryTree <Type> & T; //BT    const BTNode<Type> *current;public:    TreeIterator(const BinaryTree <Type> & BT)        : T(BT), current(NULL) { }    virtual ~TreeIterator() { }    virtual void First() = 0;    virtual void operator ++ () = 0;    operator bool() { return current != NULL; }    const Type operator()()const {        if (current)            return current->data;        return (Type)0;    }};template <class Type> struct StkNode {    //Stack node definition    const BTNode <Type> *Node;  //Node Address    int PopTime;                                        //Counter    StkNode(const BTNode <Type> *N = NULL) : Node(N), PopTime(0) { }};template <class Type> class PostOrder : public TreeIterator <Type> {    bool renew;public:    PostOrder(const BinaryTree <Type> & BT) :TreeIterator(BT) { renew = false; }    ~PostOrder() { }    void First();    //Seek to the first node in postorder traversal    void operator ++ ();    //Seek to the successorprotected:    stack<StkNode<Type>> st;     //Active record stack};template <class Type>void PostOrder<Type>::First() {    current = T.root;    while (!st.empty()) {        st.pop();    }    renew = true;    operator++();}template <class Type>void PostOrder<Type>::operator ++() {    if (!renew && current == T.root && st.empty()) {        current = NULL;        return;    }    renew = false;    const BTNode<Type> *p = current;    StkNode<Type> w;    do {        // Here, you must add necessary statements to set pointer current to the right posotion        if (st.empty() || (st.top().Node->left != p && st.top().Node->right != current))            while (p) {                st.push(StkNode<Type>(p));                p = p->left;            }        w = st.top();        st.pop();        if (++w.PopTime == 2) {            current = w.Node;            return;        }        st.push(w);        if (w.Node->right) {            p = w.Node->right;        }    } while (true);}int main() {    BTNode<int> *p = new BTNode<int>(6);    p->left = new BTNode<int>(4);    p->right = new BTNode<int>(10);    p->left->left = new BTNode<int>(2);    p->right->left = new BTNode<int>(8);    p->right->right = new BTNode<int>(12);    BinaryTree<int> T(p);    PostOrder<int> it(T);    for (it.First(); it; ++it) {        std::cout << it() << std::endl;    }    system("pause");    return 0;}