二叉树的三种遍历方法（C++）

其他 2020-04-21 16:34:31 阅读次数: 0

0.二叉树的创建

0.1 二叉树节点结构

下为简单二叉树，没有考虑指向父节点的指针等。

struct BinaryTreeNode 
{
    int                    m_nValue; //节点data值
    BinaryTreeNode*        m_pLeft;  //左子节点
    BinaryTreeNode*        m_pRight; //右子节点
};

0.2 二叉树节点的创建

//新建一个父节点
BinaryTreeNode* CreateBinaryTreeNode(int value)
{
    BinaryTreeNode* pNode = new BinaryTreeNode();
    pNode->m_nValue = value;
    pNode->m_pLeft = nullptr;
    pNode->m_pRight = nullptr;

    return pNode;
}

0.3 二叉树节点的连接

//父节点连接左右子节点
void ConnectTreeNodes(BinaryTreeNode* pParent, BinaryTreeNode* pLeft, BinaryTreeNode* pRight)
{
    if(pParent != nullptr)
    {
        pParent->m_pLeft = pLeft;
        pParent->m_pRight = pRight;
    }
}

0.4 二叉树的删除

//递归调用删除整个树
void DestroyTree(BinaryTreeNode* pRoot)
{
    if(pRoot != nullptr)
    {
        BinaryTreeNode* pLeft = pRoot->m_pLeft;
        BinaryTreeNode* pRight = pRoot->m_pRight;

        delete pRoot;
        pRoot = nullptr;

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

1.前序遍历

前序遍历：先遍历根节点，再遍历左子树，最后遍历右子树（根-左-右）

测试代码：

// ====================测试代码====================
void Test(const char* testName, BinaryTreeNode* pRoot, 
    vector<int> expectedPre, vector<int> expectedIn, vector<int> expectedPost, int expectedLength)
{
    if (testName != nullptr)
        printf("%s begins: ", testName);

    vector<int> treeNodes;
    TraverseBinaryTree(pRoot, treeNodes);
    int length = treeNodes.size();

    bool flag = true;
    for (int i = 0; i < length && length == expectedLength; ++i)
    {
        if (treeNodes[i] != expectedPre[i])  //遍历预测值在这里改一下就行
            flag = false;
    }
    
    if (flag)
        printf("Passed.\n");
    else
        printf("Failed.\n");
}

// 1.满二叉树
//            10
//          /    \
//         6      14
//        /\      /\
//       4  8   12  16
void Test1()
{
    BinaryTreeNode* pNode10 = CreateBinaryTreeNode(10);
    BinaryTreeNode* pNode6 = CreateBinaryTreeNode(6);
    BinaryTreeNode* pNode14 = CreateBinaryTreeNode(14);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode8 = CreateBinaryTreeNode(8);
    BinaryTreeNode* pNode12 = CreateBinaryTreeNode(12);
    BinaryTreeNode* pNode16 = CreateBinaryTreeNode(16);

    ConnectTreeNodes(pNode10, pNode6, pNode14);
    ConnectTreeNodes(pNode6, pNode4, pNode8);
    ConnectTreeNodes(pNode14, pNode12, pNode16);

    vector<int> expectedPre = {10, 6, 4, 8, 14, 12, 16};
    vector<int> expectedIn = {4, 6, 8, 10, 12, 14, 16};
    vector<int> expectedPost = {4, 8, 6, 12, 16, 14, 10};

    Test("Test1", pNode10, expectedPre, expectedIn, expectedPost, 7);

    DestroyTree(pNode10);
}

//               5
//              /
//             4
//            /
//           3
//          /
//         2
//        /
//       1
void Test2()
{
    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);

    ConnectTreeNodes(pNode5, pNode4, nullptr);
    ConnectTreeNodes(pNode4, pNode3, nullptr);
    ConnectTreeNodes(pNode3, pNode2, nullptr);
    ConnectTreeNodes(pNode2, pNode1, nullptr);

    vector<int> expectedPre = {5, 4, 3, 2, 1};
    vector<int> expectedIn = {1, 2, 3, 4, 5};
    vector<int> expectedPost = {1, 2, 3, 4, 5};

    Test("Test2", pNode5, expectedPre, expectedIn, expectedPost, 5);

    DestroyTree(pNode5);
}

// 1
//  \
//   2
//    \
//     3
//      \
//       4
//        \
//         5
void Test3()
{
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);
    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);

    ConnectTreeNodes(pNode1, nullptr, pNode2);
    ConnectTreeNodes(pNode2, nullptr, pNode3);
    ConnectTreeNodes(pNode3, nullptr, pNode4);
    ConnectTreeNodes(pNode4, nullptr, pNode5);

    vector<int> expectedPre = {1, 2, 3, 4, 5};
    vector<int> expectedIn = { 1, 2, 3, 4, 5 };
    vector<int> expectedPost = {5, 4, 3, 2, 1};

    Test("Test3", pNode1, expectedPre, expectedIn, expectedPost, 5);

    DestroyTree(pNode1);
}

// 树中只有1个结点
void Test4()
{
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);

    vector<int> expectedPre = {1};
    vector<int> expectedIn = {1};
    vector<int> expectedPost = {1};

    Test("Test4", pNode1, expectedPre, expectedIn, expectedPost, 1);

    DestroyTree(pNode1);
}

// 树中没有结点
void Test5()
{
    vector<int> expectedPre = {};
    vector<int> expectedIn = {};
    vector<int> expectedPost = {};

    Test("Test5", nullptr, expectedPre, expectedIn, expectedPost, 0);
}

int main(int argc, char* argv[])
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();

    return 0;
}
前序遍历测试代码

1.1 基于递归实现

void TraverseBinaryTree(BinaryTreeNode* pRoot, vector<int>& treeNodes)
{
    if (pRoot == nullptr)
        return;

    //前序遍历
    treeNodes.push_back(pRoot->m_nValue);
    TraverseBinaryTree(pRoot->m_pLeft, treeNodes);
    TraverseBinaryTree(pRoot->m_pRight, treeNodes);
}

1.2 基于迭代实现

2.中序遍历

中序遍历：先遍历左子树，再遍历根节点，最后遍历右子树（左-根-右）

 测试代码：

// ====================测试代码====================
void Test(const char* testName, BinaryTreeNode* pRoot, 
    vector<int> expectedPre, vector<int> expectedIn, vector<int> expectedPost, int expectedLength)
{
    if (testName != nullptr)
        printf("%s begins: ", testName);

    vector<int> treeNodes;
    TraverseBinaryTree(pRoot, treeNodes);
    int length = treeNodes.size();

    bool flag = true;
    for (int i = 0; i < length && length == expectedLength; ++i)
    {
        if (treeNodes[i] != expectedIn[i])  //遍历预测值在这里改一下就行
            flag = false;
    }
    
    if (flag)
        printf("Passed.\n");
    else
        printf("Failed.\n");
}

// 1.满二叉树
//            10
//          /    \
//         6      14
//        /\      /\
//       4  8   12  16
void Test1()
{
    BinaryTreeNode* pNode10 = CreateBinaryTreeNode(10);
    BinaryTreeNode* pNode6 = CreateBinaryTreeNode(6);
    BinaryTreeNode* pNode14 = CreateBinaryTreeNode(14);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode8 = CreateBinaryTreeNode(8);
    BinaryTreeNode* pNode12 = CreateBinaryTreeNode(12);
    BinaryTreeNode* pNode16 = CreateBinaryTreeNode(16);

    ConnectTreeNodes(pNode10, pNode6, pNode14);
    ConnectTreeNodes(pNode6, pNode4, pNode8);
    ConnectTreeNodes(pNode14, pNode12, pNode16);

    vector<int> expectedPre = {10, 6, 4, 8, 14, 12, 16};
    vector<int> expectedIn = {4, 6, 8, 10, 12, 14, 16};
    vector<int> expectedPost = {4, 8, 6, 12, 16, 14, 10};

    Test("Test1", pNode10, expectedPre, expectedIn, expectedPost, 7);

    DestroyTree(pNode10);
}

//               5
//              /
//             4
//            /
//           3
//          /
//         2
//        /
//       1
void Test2()
{
    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);

    ConnectTreeNodes(pNode5, pNode4, nullptr);
    ConnectTreeNodes(pNode4, pNode3, nullptr);
    ConnectTreeNodes(pNode3, pNode2, nullptr);
    ConnectTreeNodes(pNode2, pNode1, nullptr);

    vector<int> expectedPre = {5, 4, 3, 2, 1};
    vector<int> expectedIn = {1, 2, 3, 4, 5};
    vector<int> expectedPost = {1, 2, 3, 4, 5};

    Test("Test2", pNode5, expectedPre, expectedIn, expectedPost, 5);

    DestroyTree(pNode5);
}

// 1
//  \
//   2
//    \
//     3
//      \
//       4
//        \
//         5
void Test3()
{
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);
    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);

    ConnectTreeNodes(pNode1, nullptr, pNode2);
    ConnectTreeNodes(pNode2, nullptr, pNode3);
    ConnectTreeNodes(pNode3, nullptr, pNode4);
    ConnectTreeNodes(pNode4, nullptr, pNode5);

    vector<int> expectedPre = {1, 2, 3, 4, 5};
    vector<int> expectedIn = { 1, 2, 3, 4, 5 };
    vector<int> expectedPost = {5, 4, 3, 2, 1};

    Test("Test3", pNode1, expectedPre, expectedIn, expectedPost, 5);

    DestroyTree(pNode1);
}

// 树中只有1个结点
void Test4()
{
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);

    vector<int> expectedPre = {1};
    vector<int> expectedIn = {1};
    vector<int> expectedPost = {1};

    Test("Test4", pNode1, expectedPre, expectedIn, expectedPost, 1);

    DestroyTree(pNode1);
}

// 树中没有结点
void Test5()
{
    vector<int> expectedPre = {};
    vector<int> expectedIn = {};
    vector<int> expectedPost = {};

    Test("Test5", nullptr, expectedPre, expectedIn, expectedPost, 0);
}

int main(int argc, char* argv[])
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();

    return 0;
}
中序遍历测试代码

2.1 基于递归实现

void TraverseBinaryTree(BinaryTreeNode* pRoot, vector<int>& treeNodes)
{
    if (pRoot == nullptr)
        return;

    //中序遍历
    TraverseBinaryTree(pRoot->m_pLeft, treeNodes);
    treeNodes.push_back(pRoot->m_nValue);
    TraverseBinaryTree(pRoot->m_pRight, treeNodes);
}

2.2 基于迭代实现

3 后序遍历

后序遍历：先遍历左子树，再遍历右子树，最后遍历根节点（左-右-根）

 测试代码：

// ====================测试代码====================
void Test(const char* testName, BinaryTreeNode* pRoot, 
    vector<int> expectedPre, vector<int> expectedIn, vector<int> expectedPost, int expectedLength)
{
    if (testName != nullptr)
        printf("%s begins: ", testName);

    vector<int> treeNodes;
    TraverseBinaryTree(pRoot, treeNodes);
    int length = treeNodes.size();

    bool flag = true;
    for (int i = 0; i < length && length == expectedLength; ++i)
    {
        if (treeNodes[i] != expectedPost[i])  //遍历预测值在这里改一下就行
            flag = false;
    }
    
    if (flag)
        printf("Passed.\n");
    else
        printf("Failed.\n");
}

// 1.满二叉树
//            10
//          /    \
//         6      14
//        /\      /\
//       4  8   12  16
void Test1()
{
    BinaryTreeNode* pNode10 = CreateBinaryTreeNode(10);
    BinaryTreeNode* pNode6 = CreateBinaryTreeNode(6);
    BinaryTreeNode* pNode14 = CreateBinaryTreeNode(14);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode8 = CreateBinaryTreeNode(8);
    BinaryTreeNode* pNode12 = CreateBinaryTreeNode(12);
    BinaryTreeNode* pNode16 = CreateBinaryTreeNode(16);

    ConnectTreeNodes(pNode10, pNode6, pNode14);
    ConnectTreeNodes(pNode6, pNode4, pNode8);
    ConnectTreeNodes(pNode14, pNode12, pNode16);

    vector<int> expectedPre = {10, 6, 4, 8, 14, 12, 16};
    vector<int> expectedIn = {4, 6, 8, 10, 12, 14, 16};
    vector<int> expectedPost = {4, 8, 6, 12, 16, 14, 10};

    Test("Test1", pNode10, expectedPre, expectedIn, expectedPost, 7);

    DestroyTree(pNode10);
}

//               5
//              /
//             4
//            /
//           3
//          /
//         2
//        /
//       1
void Test2()
{
    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);

    ConnectTreeNodes(pNode5, pNode4, nullptr);
    ConnectTreeNodes(pNode4, pNode3, nullptr);
    ConnectTreeNodes(pNode3, pNode2, nullptr);
    ConnectTreeNodes(pNode2, pNode1, nullptr);

    vector<int> expectedPre = {5, 4, 3, 2, 1};
    vector<int> expectedIn = {1, 2, 3, 4, 5};
    vector<int> expectedPost = {1, 2, 3, 4, 5};

    Test("Test2", pNode5, expectedPre, expectedIn, expectedPost, 5);

    DestroyTree(pNode5);
}

// 1
//  \
//   2
//    \
//     3
//      \
//       4
//        \
//         5
void Test3()
{
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);
    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);

    ConnectTreeNodes(pNode1, nullptr, pNode2);
    ConnectTreeNodes(pNode2, nullptr, pNode3);
    ConnectTreeNodes(pNode3, nullptr, pNode4);
    ConnectTreeNodes(pNode4, nullptr, pNode5);

    vector<int> expectedPre = {1, 2, 3, 4, 5};
    vector<int> expectedIn = { 1, 2, 3, 4, 5 };
    vector<int> expectedPost = {5, 4, 3, 2, 1};

    Test("Test3", pNode1, expectedPre, expectedIn, expectedPost, 5);

    DestroyTree(pNode1);
}

// 树中只有1个结点
void Test4()
{
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);

    vector<int> expectedPre = {1};
    vector<int> expectedIn = {1};
    vector<int> expectedPost = {1};

    Test("Test4", pNode1, expectedPre, expectedIn, expectedPost, 1);

    DestroyTree(pNode1);
}

// 树中没有结点
void Test5()
{
    vector<int> expectedPre = {};
    vector<int> expectedIn = {};
    vector<int> expectedPost = {};

    Test("Test5", nullptr, expectedPre, expectedIn, expectedPost, 0);
}

int main(int argc, char* argv[])
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();

    return 0;
}
后序遍历测试代码

3.1 基于递归实现

void TraverseBinaryTree(BinaryTreeNode* pRoot, vector<int>& treeNodes)
{
    if (pRoot == nullptr)
        return;

    //后序遍历
    TraverseBinaryTree(pRoot->m_pLeft, treeNodes);
    TraverseBinaryTree(pRoot->m_pRight, treeNodes);
    treeNodes.push_back(pRoot->m_nValue);
}

3.2 基于迭代实现

完整代码：

// 二叉树的三种遍历
// 1.前序遍历
// 2.中序遍历
// 3.后序遍历

#include <cstdio>
#include <vector>
#include "BinaryTree.h"

using namespace std;

//注意：改动此函数即可
void TraverseBinaryTree(BinaryTreeNode* pRoot, vector<int>& treeNodes)
{
    if (pRoot == nullptr)
        return;

    //前序遍历
    treeNodes.push_back(pRoot->m_nValue);
    TraverseBinaryTree(pRoot->m_pLeft, treeNodes);
    TraverseBinaryTree(pRoot->m_pRight, treeNodes);
}

// ====================测试代码====================
void Test(const char* testName, BinaryTreeNode* pRoot, 
    vector<int> expectedPre, vector<int> expectedIn, vector<int> expectedPost, int expectedLength)
{
    if (testName != nullptr)
        printf("%s begins: ", testName);

    vector<int> treeNodes;
    TraverseBinaryTree(pRoot, treeNodes);
    int length = treeNodes.size();

    bool flag = true;
    for (int i = 0; i < length && length == expectedLength; ++i)
    {
        if (treeNodes[i] != expectedPre[i])  //注意：遍历预测值在这里改一下就行
            flag = false;
    }
    
    if (flag)
        printf("Passed.\n");
    else
        printf("Failed.\n");
}

// 1.满二叉树
//            10
//          /    \
//         6      14
//        /\      /\
//       4  8   12  16
void Test1()
{
    BinaryTreeNode* pNode10 = CreateBinaryTreeNode(10);
    BinaryTreeNode* pNode6 = CreateBinaryTreeNode(6);
    BinaryTreeNode* pNode14 = CreateBinaryTreeNode(14);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode8 = CreateBinaryTreeNode(8);
    BinaryTreeNode* pNode12 = CreateBinaryTreeNode(12);
    BinaryTreeNode* pNode16 = CreateBinaryTreeNode(16);

    ConnectTreeNodes(pNode10, pNode6, pNode14);
    ConnectTreeNodes(pNode6, pNode4, pNode8);
    ConnectTreeNodes(pNode14, pNode12, pNode16);

    vector<int> expectedPre = {10, 6, 4, 8, 14, 12, 16};
    vector<int> expectedIn = {4, 6, 8, 10, 12, 14, 16};
    vector<int> expectedPost = {4, 8, 6, 12, 16, 14, 10};

    Test("Test1", pNode10, expectedPre, expectedIn, expectedPost, 7);

    DestroyTree(pNode10);
}

//               5
//              /
//             4
//            /
//           3
//          /
//         2
//        /
//       1
void Test2()
{
    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);

    ConnectTreeNodes(pNode5, pNode4, nullptr);
    ConnectTreeNodes(pNode4, pNode3, nullptr);
    ConnectTreeNodes(pNode3, pNode2, nullptr);
    ConnectTreeNodes(pNode2, pNode1, nullptr);

    vector<int> expectedPre = {5, 4, 3, 2, 1};
    vector<int> expectedIn = {1, 2, 3, 4, 5};
    vector<int> expectedPost = {1, 2, 3, 4, 5};

    Test("Test2", pNode5, expectedPre, expectedIn, expectedPost, 5);

    DestroyTree(pNode5);
}

// 1
//  \
//   2
//    \
//     3
//      \
//       4
//        \
//         5
void Test3()
{
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);
    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);

    ConnectTreeNodes(pNode1, nullptr, pNode2);
    ConnectTreeNodes(pNode2, nullptr, pNode3);
    ConnectTreeNodes(pNode3, nullptr, pNode4);
    ConnectTreeNodes(pNode4, nullptr, pNode5);

    vector<int> expectedPre = {1, 2, 3, 4, 5};
    vector<int> expectedIn = { 1, 2, 3, 4, 5 };
    vector<int> expectedPost = {5, 4, 3, 2, 1};

    Test("Test3", pNode1, expectedPre, expectedIn, expectedPost, 5);

    DestroyTree(pNode1);
}

// 树中只有1个结点
void Test4()
{
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);

    vector<int> expectedPre = {1};
    vector<int> expectedIn = {1};
    vector<int> expectedPost = {1};

    Test("Test4", pNode1, expectedPre, expectedIn, expectedPost, 1);

    DestroyTree(pNode1);
}

// 树中没有结点
void Test5()
{
    vector<int> expectedPre = {};
    vector<int> expectedIn = {};
    vector<int> expectedPost = {};

    Test("Test5", nullptr, expectedPre, expectedIn, expectedPost, 0);
}

int main(int argc, char* argv[])
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();

    return 0;
}
View Code 
//==================================================================
// 《剑指Offer——名企面试官精讲典型编程题》代码
// 作者：何海涛
//==================================================================

#pragma once

struct BinaryTreeNode 
{
    int                    m_nValue; //节点data值
    BinaryTreeNode*        m_pLeft;  //左子节点
    BinaryTreeNode*        m_pRight; //右子节点
};

__declspec( dllexport ) BinaryTreeNode* CreateBinaryTreeNode(int value);
__declspec( dllexport ) void ConnectTreeNodes(BinaryTreeNode* pParent, BinaryTreeNode* pLeft, BinaryTreeNode* pRight);
__declspec( dllexport ) void PrintTreeNode(const BinaryTreeNode* pNode);
__declspec( dllexport ) void PrintTree(const BinaryTreeNode* pRoot);
__declspec( dllexport ) void DestroyTree(BinaryTreeNode* pRoot);
BinaryTree.h 
//==================================================================
// 《剑指Offer——名企面试官精讲典型编程题》代码
// 作者：何海涛
//==================================================================

#include <cstdio>
#include "BinaryTree.h"

//新建一个父节点
BinaryTreeNode* CreateBinaryTreeNode(int value)
{
    BinaryTreeNode* pNode = new BinaryTreeNode();
    pNode->m_nValue = value;
    pNode->m_pLeft = nullptr;
    pNode->m_pRight = nullptr;

    return pNode;
}

//父节点连接左右子节点
void ConnectTreeNodes(BinaryTreeNode* pParent, BinaryTreeNode* pLeft, BinaryTreeNode* pRight)
{
    if(pParent != nullptr)
    {
        pParent->m_pLeft = pLeft;
        pParent->m_pRight = pRight;
    }
}

//打印当前父节点以及左右子节点
void PrintTreeNode(const BinaryTreeNode* pNode)
{
    if(pNode != nullptr)
    {
        printf("value of this node is: %d\n", pNode->m_nValue);

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

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

    printf("\n");
}

//递归调用打印整个二叉树
void PrintTree(const BinaryTreeNode* pRoot)
{
    PrintTreeNode(pRoot);

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

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

//递归调用删除整个树
void DestroyTree(BinaryTreeNode* pRoot)
{
    if(pRoot != nullptr)
    {
        BinaryTreeNode* pLeft = pRoot->m_pLeft;
        BinaryTreeNode* pRight = pRoot->m_pRight;

        delete pRoot;
        pRoot = nullptr;

        DestroyTree(pLeft);
        DestroyTree(pRight);
    }
}
BinaryTree.cpp

代码与图参考：

[1] 剑指offer（第二版）, 何海涛, 2011.

[2] 数据结构（C++语言版）, 邓俊辉, 2010.

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