二叉树的各种遍历

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    // 前序：访问根节点--->访问根节点的左子树--->访问根节点的右子树    void _PreOrder(Node* pRoot)      {        if (pRoot)        {            cout << pRoot->_value << " ";            _PreOrder(pRoot->_pLeft);            _PreOrder(pRoot->_pRight);        }    }    //前序遍历非递归    void _PreOrder_Nor(Node*pRoot)    {        if (NULL == pRoot)            return;        stack<Node*>s;        s.push(pRoot);        while (!s.empty())        {            Node*pCur = s.top();            cout << pCur->_value << " ";            s.pop();            if (pCur->_pRight)                s.push(pCur->_pRight);            if (pCur->_pLeft)                s.push(pCur->_pLeft);        }    }    //中序遍历递归    void _InOrder(Node* pRoot)    {        if (pRoot)        {             _InOrder(pRoot->_pLeft);            cout << pRoot->_value << " ";            _InOrder(pRoot->_pRight);        }    }    //中序遍历非递归    void _InOrder_Nor(Node*pRoot)    {        if (NULL == pRoot)            return;        stack<Node*>s;        Node*pCur = pRoot;        while (pCur || !s.empty())        {            while (pCur)            {  // 找到最左边的孩子，并把所经过路径的结点保存下来                s.push(pCur);                pCur = pCur->_pLeft;            }            //出了内层循环，pCur为空，栈顶元素为最左边的孩子            pCur = s.top();            cout << pCur->_value << " ";            s.pop();            pCur = pCur->_pRight;        }    }    // 后序遍历：遍历根的左子树-->遍历根的右子树-->遍历根节点    void _PostOrder(Node* pRoot)    {        if (pRoot)        {            _PostOrder(pRoot->_pLeft);            _PostOrder(pRoot->_pRight);            cout << pRoot->_value << " ";        }    }    //后序遍历非递归    void _PostOrder_Nor(Node*pRoot)    {        if (NULL == pRoot)            return;        stack<Node*>s;        Node*pCur = pRoot;        Node*Prev = NULL;//保存上次入栈的结点        while (pCur || !s.empty())        {            while (pCur)            {  // 找到最左边的孩子，并把所经过路径的结点保存下来                s.push(pCur);                pCur = pCur->_pLeft;            }            Node*pTop = s.top();            if (NULL == pTop->_pRight || Prev == pTop->_pRight)//没有Prev == pTop->_pRight会4256666666......会死循环下去            {   //Prev == pTop->_pRight右已经访问过了，才能访问当前的根                    //NULL == pTop->_pRight                  cout << pTop->_value << " ";                Prev = pTop; //保存上次入栈的结点                s.pop();            }            else            {                pCur = pTop;//pCur在while出来之后为NULL，所以要更新pCur的值，少了这句，崩溃                pCur = pCur->_pRight;//将右子树当做一颗新的树去访问            }        }    }    // 层序遍历    void _LevelOrder(Node*pRoot)//******考点********队列***    {        if (NULL == pRoot)            return;        queue<Node*>q;        q.push(pRoot);//保存的是结点的地址，地址出了队列，但是树并没有改变        while (!q.empty())        {            Node*pcur = q.front();            cout << pcur->_value << " ";            if (pcur->_pLeft)//左不为空入队列            {                q.push(pcur->_pLeft);            }            if (pcur->_pRight)//右不为空入队列            {                q.push(pcur->_pRight);            }            q.pop();        }        cout << endl;    }
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