二叉树的遍历方式（递归和非递归版本）

二叉树结构体：

struct BinaryTreeNode 
{
    int                    m_nValue; 
    BinaryTreeNode*        m_pLeft;  
    BinaryTreeNode*        m_pRight; 
};

二叉树创建：

BinaryTreeNode* CreateBinaryTreeNode(int value)
{
    BinaryTreeNode* pNode = new BinaryTreeNode();
    pNode->m_nValue = value;
    pNode->m_pLeft = NULL;
    pNode->m_pRight = NULL;

    return pNode;
}

打印二叉树：

void PrintTreeNode(BinaryTreeNode* pNode)
{
    if(pNode != NULL)
    {
        printf("value of this node is: %d
", pNode->m_nValue);

        if(pNode->m_pLeft != NULL)
            printf("value of its left child is: %d.
", pNode->m_pLeft->m_nValue);
        else
            printf("left child is null.
");

        if(pNode->m_pRight != NULL)
            printf("value of its right child is: %d.
", pNode->m_pRight->m_nValue);
        else
            printf("right child is null.
");
    }
    else
    {
        printf("this node is null.
");
    }

    printf("
");
}

void PrintTree(BinaryTreeNode* pRoot)
{
    PrintTreeNode(pRoot);

    if(pRoot != NULL)
    {
        if(pRoot->m_pLeft != NULL)
            PrintTree(pRoot->m_pLeft);

        if(pRoot->m_pRight != NULL)
            PrintTree(pRoot->m_pRight);
    }
}

销毁二叉树：

void DestroyTree(BinaryTreeNode* pRoot)
{
    if(pRoot != NULL)
    {
        BinaryTreeNode* pLeft = pRoot->m_pLeft;
        BinaryTreeNode* pRight = pRoot->m_pRight;

        delete pRoot;
        pRoot = NULL;

        DestroyTree(pLeft);
        DestroyTree(pRight);
    }
}

遍历方式（前序、中序、后序）：

//前序遍历 根节点->左节点->右节点
void pre_traverse(BinaryTreeNode* pRoot)
{
    if (pRoot)
    {
        printf(" %d", pRoot->m_nValue);
        if (pRoot->m_pLeft)
            pre_traverse(pRoot->m_pLeft);
        if (pRoot->m_pRight)
            pre_traverse(pRoot->m_pRight);
    }
}

//前序遍历的非递归实现
void pre_traverse_stack(BinaryTreeNode* pRoot)
{
    if (NULL == pRoot)
        return;

    stack<BinaryTreeNode*> Bnode;
    BinaryTreeNode* node_pop = NULL; //保存出栈节点
    BinaryTreeNode* pcurrent = pRoot; //访问当前节点

    //直至当前节点为空或栈为空时,结束循环
    while (pcurrent||!Bnode.empty())
    {
        //若左子结点非空,则不断输出左子结点数值
        while (pcurrent)
        {
            printf(" %d", pcurrent->m_nValue);
            Bnode.push(pcurrent);
            pcurrent = pcurrent->m_pLeft;
        }
        //记录父节点，顶出父节点,对父节点的右节点进行操作
        if (!Bnode.empty())
        {
            pcurrent = Bnode.top();
            Bnode.pop();
            pcurrent = pcurrent->m_pRight;
        }
    }
}

//中序遍历 左节点->根节点->右节点
void mid_traverse(BinaryTreeNode* pRoot)
{
    if (pRoot)
    {
        if (pRoot->m_pLeft)
            mid_traverse(pRoot->m_pLeft);
        printf(" %d", pRoot->m_nValue);
        if (pRoot->m_pRight)
            mid_traverse(pRoot->m_pRight);
    }
}

//中序遍历的非递归版本
void mid_traverse_stack(BinaryTreeNode* pRoot)
{
    if (NULL == pRoot)
        return;

    stack<BinaryTreeNode*> Bnode;
    BinaryTreeNode* pcurrent = pRoot; //访问当前节点

    while (pcurrent || !Bnode.empty())
    {
        while (pcurrent)
        {
            Bnode.push(pcurrent);
            pcurrent = pcurrent->m_pLeft;
        }
        if (!Bnode.empty())
        {
            pcurrent = Bnode.top();
            printf(" %d", pcurrent->m_nValue);
            Bnode.pop();
            pcurrent = pcurrent->m_pRight;
        }
    }
}

//后续遍历 左节点->右节点->根节点
void beh_traverse(BinaryTreeNode* pRoot)
{
    if (pRoot)
    {
        if (pRoot->m_pLeft)
            beh_traverse(pRoot->m_pLeft);
        if (pRoot->m_pRight)
            beh_traverse(pRoot->m_pRight);
        printf(" %d", pRoot->m_nValue);
    }
}

//后序遍历的非递归版本
void beh_traverse_stack(BinaryTreeNode* pRoot)
{
    if (NULL == pRoot)
        return;

    stack<BinaryTreeNode*> Bnode;
    BinaryTreeNode* pre_node = NULL; //前次访问节点
    BinaryTreeNode* pcurrent = NULL; //访问当前节点

    Bnode.push(pRoot);
    while (!Bnode.empty())
    {
        pcurrent = Bnode.top();
        //如果当前节点没有子节点或者子节点已经被访问过,则输出其相应数值
        if ((pcurrent->m_pLeft == NULL&&pcurrent->m_pRight == NULL) ||
            (pre_node != NULL && (pre_node == pcurrent->m_pLeft || pre_node == pcurrent->m_pRight)))
        {
            printf(" %d", pcurrent->m_nValue);
            Bnode.pop();
            pre_node = pcurrent;
        }
        else
        {
            if (pcurrent->m_pRight)
                Bnode.push(pcurrent->m_pRight);
            if (pcurrent->m_pLeft)
                Bnode.push(pcurrent->m_pLeft);
        }
    }
}