二叉樹前序、中序和后序的非遞歸遍歷

非遞歸遍歷二叉樹利用棧的先進先出特點完成實現

前序比較好理解先壓根入棧，在while里面訪問根，根出棧，再壓入右子樹，左子樹，這樣的遍歷二叉樹就是前序遍歷了。

void PrevOrdr_NonR()

{

    stack<BinaryTreeNode<T>*> s;

    s.push(_root);

    while(!s.empty())

    {

       BinaryTreeNode<T>* top = s.top();

       s.pop();

       cout<<top->_data<<" ";

       if(top->_right)

           s.push(top->_right);

       if(top->_left)

           s.push(top->_left); 

    }

    cout<<endl;

}

中序的遍歷順序是左子樹、根節點、右子樹。

void InOreder_NonR()

{

    stack<BinaryTreeNode<T>*> s;

    BinaryTreeNode<T>* cur = _root;

    while(cur || !s.empty())

    {

        while(cur)//把左路徑的節點全部壓入棧

        {

            s.push(cur);

            cur = cur->_left;

        }

        if(!s.empty())

        {

            BinaryTreeNode<T>* top = s.top();

            s.pop();

            cout<<tmp->_data<<" ";

            cur = cur->_right;//把cur指向最后一個左節點的右節點

        }

    }

    cout<<endl;

}

后序遍歷是左子樹、右子樹、根節點。

void PostOrder_NonR()

{

    stack<BinaryTreeNode<T>*> s;

    BinaryTreeNode<T>* cur = _root;

    BinaryTreeNode<T>* prevVisited = NULL;

    while(cur || s.empty())

    {

        while(cur)//左路徑的節點入棧

        {

            s.push(cur);

            cur = cur->_left;

        }

        BinaryTreeNode<T>* top = s.top();

        if(top->_right == NULL || top->right == preVisited)

        //當子樹遍歷之后回退到上一個沒有遍歷的子樹

        {

            cout<<top->_data<<" ";

            preVisited = tmp;

            s.pop();

        }

        else

        {

            cur = cur->left;//把cur指向右子樹繼續尋找左節點

        }

    }

}