二叉树

递归是利用栈桢来实现的，而非递归则是用Stack来实现，递归相比较非递归来说，缺陷在栈桢储存在栈上，有可能发生栈溢出。
二叉树代码如下

#pragma once#include <queue>#include <stack>template<class T>struct BinaryTreeNode{    BinaryTreeNode<T>* _left;    BinaryTreeNode<T>* _right;    T _data;    BinaryTreeNode(const T& x)        :_left(NULL)        ,_right(NULL)        ,_data(x)    {}};template<class T>class BinaryTree{    typedef BinaryTreeNode<T> Node;public:    BinaryTree()        :_root(NULL)    {}    BinaryTree(T* a, size_t n, const T& invalid)    {        size_t index = 0;        _root = CreateTree(a, n, invalid, index);    }    Node* _Copy(Node* root)    {        if (root == NULL)            return NULL;        Node* newRoot = new Node(root->_data);        newRoot->_left = _Copy(root->_left);        newRoot->_right = _Copy(root->_right);        return newRoot;    }    BinaryTree(const BinaryTree<T>& t)    {        _root = _Copy(t._root);    }    // t1 = t2    /*BinaryTree<T>& operator=(const BinaryTree<T>& t)    {        if (this != &t)        {            Destroy(_root);            _root = _Copy(t._root);        }        return *this;    }*/    BinaryTree<T>& operator=(BinaryTree<T> t)    {        swap(_root, t._root);        return *this;    }    ~BinaryTree()    {        Destroy(_root);    }    void Destroy(Node* root)    {        if (root == NULL)            return;        Destroy(root->_left);        Destroy(root->_right);        delete root;    }    void PrevOrder()    {        _PrevOrder(_root);        cout<<endl;    }    void PrevOrderNonR()    {        stack<Node*> s;        Node* cur = _root;        while (cur || !s.empty())        {            while (cur)            {                cout<<cur->_data<<" ";                s.push(cur);                cur = cur->_left;            }            // top从栈取出来表示这个节点的左子树访问过了            // 剩余右子树还没访问，循环子问题访问右树            Node* top = s.top();            s.pop();            // 子问题的方式访问右树            cur = top->_right;        }        cout<<endl;    }    void InOrder()    {        _InOrder(_root);        cout<<endl;    }    void InOrderNonR()    {        Node* cur = _root;        stack<Node*> s;        while (cur || !s.empty())        {            while (cur)            {                s.push(cur);                cur = cur->_left;            }            Node* top = s.top();            s.pop();            cout<<top->_data<<" ";            // 子问题            cur = top->_right;        }    }    void PostOrderNonR()    {        Node* cur = _root;        stack<Node*> s;        Node* prev = NULL;        while (cur || !s.empty())        {            while (cur)            {                s.push(cur);                cur = cur->_left;            }            Node* front = s.top();            if (front->_right == NULL || front->_right == prev)            {                cout<<front->_data<<" ";                prev = front;                s.pop();            }            else            {                // 子问题                cur = front->_right;            }        }        cout<<endl;    }    void LevelOrder()    {        queue<Node*> q;        if (_root)            q.push(_root);        while (!q.empty())        {            Node* front = q.front();            cout<<front->_data<<" ";            if (front->_left)                q.push(front->_left);            if (front->_right)                q.push(front->_right);            q.pop();        }        cout<<endl;    }    size_t Size()    {        return _Size(_root);    }    size_t LeafSize()    {        return _LeafSize(_root);    }    size_t GetKLevel(size_t k)    {        assert(k > 0);        return _GetKLevel(_root, k);    }    size_t Depth()    {        return _Depth(_root);    }    Node* Find(const T& x)    {        return _Find(_root, x);    }    // 不关注增删查改--没有意义protected:    Node* _Find(Node* root, const T& x)    {        if(root == NULL)            return NULL;        if (root->_data == x)            return root;        Node* ret = _Find(root->_left, x);        if (ret)            return ret;        return _Find(root->_right, x);    }    size_t _Depth(Node* root)    {        if (root == NULL)            return 0;        if (root->_left == NULL && root->_right == NULL)            return 1;        size_t left = _Depth(root->_left);        size_t right = _Depth(root->_right);        return left > right ? left+1 : right+1;    }    size_t _GetKLevel(Node* root, size_t k)    {        if (root == NULL)            return 0;        if (k == 1)            return 1;        return _GetKLevel(root->_left, k-1) + _GetKLevel(root->_right, k-1);    }    size_t _LeafSize(Node* root)    {        if (root == NULL)        {            return 0;        }        if (root->_left == NULL && root->_right == NULL)        {            return 1;        }        return _LeafSize(root->_left) + _LeafSize(root->_right);    }    void _InOrder(Node* root)    {        if (root == NULL)            return;        _InOrder(root->_left);        cout<<root->_data<<" ";        _InOrder(root->_right);    }    size_t _Size(Node* root)    {        if (root == NULL)            return 0;        return _Size(root->_left) + _Size(root->_right) +1;    }    void _PrevOrder(Node* root)    {        if (root == NULL)            return;        cout<<root->_data<<" ";        _PrevOrder(root->_left);        _PrevOrder(root->_right);    }    // 构建当前树或者子树    Node* CreateTree(T* a, size_t n, const T& invalid, size_t& index)    {        Node* root = NULL;        if (index < n && a[index] != invalid)        {            root = new Node(a[index]);            root->_left = CreateTree(a, n, invalid, ++index);            root->_right = CreateTree(a, n, invalid, ++index);        }        return root;    }protected:    Node* _root;};void TestBinaryTree(){    int array [10] = {1, 2, 3, '#', '#', 4, '#', '#', 5, 6};    BinaryTree<int> t1(array, sizeof(array)/sizeof(array[0]), '#');    t1.PrevOrder();    BinaryTree<int> t2(t1);    t2.PrevOrderNonR();    //t1.PrevOrderNonR();    //t1.PostOrderNonR();    //t1.InOrder();    //t1.LevelOrder();    //cout<<"Size?"<<t1.Size()<<endl;    //cout<<"K Level?"<<t1.GetKLevel(3)<<endl;    //cout<<"K Level?"<<t1.GetKLevel(4)<<endl;    //cout<<"Leaf Size?"<<t1.LeafSize()<<endl;    //cout<<"Depth?"<<t1.Depth()<<endl;}