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

BinaryTreeNode* Convert(BinaryTreeNode* pRootOftree)
{
    BinaryTreeNode* pLastNodeOfList = NULL;
    ConvertNode(pRootOftree, &pLastNodeOfList);

    //pLastNodeOfList指向双向链表的尾结点
    //我们需要返回头结点
    BinaryTreeNode* pHeadOfList = pLastNodeOfList;
    while(pLastNodeOfList != NULL && pLastNodeOfList->m_pLeft != NULL)
        pHeadOfList = pHeadOfList->m_pLeft;

    return pHeadOfList;
}

void ConvertNode(BinaryTreeNode* pNode, BinaryTreeNode** pLastNodeOfList)
{
    if(pNode == NULL)
        return;

    BinaryTreeNode* pCurrent = pNode;

    if(pCurrent->m_pLeft != NULL)
        ConvertNode(pCurrent->m_pLeft, pLastNodeOfList);

    //注意双向
    pCurrent->m_pLeft = pCurrent;
    if(*pLastNodeOfList != NULL)
        (*pLastNodeOfList)->m_pRight = pCurrent;

    *pLastNodeOfList = pCurrent;

    if(pCurrent->m_pRight != NULL)
        ConvertNode(pCurrent->m_pRight, pLastNodeOfList);
}

// ====================测试代码====================
void PrintDoubleLinkedList(BinaryTreeNode* pHeadOfList)
{
    BinaryTreeNode* pNode = pHeadOfList;

    printf("The nodes from left to right are:\n");
    while(pNode != NULL)
    {
        printf("%d\t", pNode->m_nValue);

        if(pNode->m_pRight == NULL)
            break;
        pNode = pNode->m_pRight;
    }

    printf("\nThe nodes from right to left are:\n");
    while(pNode != NULL)
    {
        printf("%d\t", pNode->m_nValue);

        if(pNode->m_pLeft == NULL)
            break;
        pNode = pNode->m_pLeft;
    }

    printf("\n");
}

void DestroyList(BinaryTreeNode* pHeadOfList)
{
    BinaryTreeNode* pNode = pHeadOfList;
    while(pNode != NULL)
    {
        BinaryTreeNode* pNext = pNode->m_pRight;

        delete pNode;
        pNode = pNext;
    }
}

void Test(char* testName, BinaryTreeNode* pRootOfTree)
{
    if(testName != NULL)
        printf("===%s begins:===\n", testName);

    PrintTree(pRootOfTree);

    BinaryTreeNode* pHeadOfList = Convert(pRootOfTree);

    PrintDoubleLinkedList(pHeadOfList);
}

//            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);

    Test("Test1", pNode10);

    DestroyList(pNode4);
}

//               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, NULL);
    ConnectTreeNodes(pNode4, pNode3, NULL);
    ConnectTreeNodes(pNode3, pNode2, NULL);
    ConnectTreeNodes(pNode2, pNode1, NULL);

    Test("Test2", pNode5);

    DestroyList(pNode1);
}

// 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, NULL, pNode2);
    ConnectTreeNodes(pNode2, NULL, pNode3);
    ConnectTreeNodes(pNode3, NULL, pNode4);
    ConnectTreeNodes(pNode4, NULL, pNode5);

    Test("Test3", pNode1);

    DestroyList(pNode1);
}

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

    DestroyList(pNode1);
}

// 树中没有结点
void Test5()
{
    Test("Test5", NULL);
}

int main(void)
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();

    return 0;
}

结果

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