Note face questions prove safety offer next binary tree node 8 ----

Title: Given a binary tree and one of the sites, how to find the next node in order traversal sequence? Node in the tree has two separate addition points to the left and right child node pointers, and a pointer pointing to the parent node.

Test Case:

• Ordinary binary tree (complete binary tree, not a complete binary tree).
• Special binary tree (all nodes have no right child of a binary tree; all nodes are not left child node of a binary tree; only one node of a binary tree; root pointer binary tree is nullptr).
• The next node in different positions (at a right child node of the current node, the leftmost child node of the right subtree of the parent node, the parent node and other cross-layer; current node is not the next node).

Test code:

void Test(char* testName, BinaryTreeNode* pNode, BinaryTreeNode* expected)
{
    if(testName != nullptr)
        printf("%s begins: ", testName);
    BinaryTreeNode* pNext = GetNext(pNode);
    if(pNext == expected)
        printf("Passed.\n");
    else
        printf("FAILED.\n");
}

//            8
//        6      10
//       5 7    9  11
void Test1_7()
{
    BinaryTreeNode* pNode8 = CreateBinaryTreeNode(8);
    BinaryTreeNode* pNode6 = CreateBinaryTreeNode(6);
    BinaryTreeNode* pNode10 = CreateBinaryTreeNode(10);
    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);
    BinaryTreeNode* pNode7 = CreateBinaryTreeNode(7);
    BinaryTreeNode* pNode9 = CreateBinaryTreeNode(9);
    BinaryTreeNode* pNode11 = CreateBinaryTreeNode(11);

    ConnectTreeNodes(pNode8, pNode6, pNode10);
    ConnectTreeNodes(pNode6, pNode5, pNode7);
    ConnectTreeNodes(pNode10, pNode9, pNode11);

    Test("Test1", pNode8, pNode9);
    Test("Test2", pNode6, pNode7);
    Test("Test3", pNode10, pNode11);
    Test("Test4", pNode5, pNode6);
    Test("Test5", pNode7, pNode8);
    Test("Test6", pNode9, pNode10);
    Test("Test7", pNode11, nullptr);

    DestroyTree(pNode8);
}

//            5
//          4
//        3
//      2
void Test8_11()
{
    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);

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

    Test("Test8", pNode5, nullptr);
    Test("Test9", pNode4, pNode5);
    Test("Test10", pNode3, pNode4);
    Test("Test11", pNode2, pNode3);

    DestroyTree(pNode5);
}

//        2
//         3
//          4
//           5
void Test12_15()
{
    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);

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

    Test("Test12", pNode5, nullptr);
    Test("Test13", pNode4, pNode5);
    Test("Test14", pNode3, pNode4);
    Test("Test15", pNode2, pNode3);

    DestroyTree(pNode2);
}

void Test16()
{
    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);

    Test("Test16", pNode5, nullptr);

    DestroyTree(pNode5);
}

This question test sites:

• Examine the candidates understanding of the binary tree traversal sequence. Only binary tree traversal algorithm to have a deep understanding of the candidates will it be possible to pinpoint the next node in order traversal of each node.
• The ability to examine the complex issues of the candidates analysis. Only candidates shown in FIG binary tree structure, a law of traversal of the nodes in order to find out by specific examples, possible to design a feasible algorithm.

Implementation code:

#include <cstdio>

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

BinaryTreeNode* GetNext(BinaryTreeNode* pNode)
{
    if(pNode == nullptr)
        return nullptr;
    BinaryTreeNode* pNext = nullptr;
    if(pNode->m_pRight != nullptr)
    {
        BinaryTreeNode* pRight = pNode->m_pRight;
        while(pRight->m_pLeft != nullptr)
            pRight = pRight->m_pLeft;
        pNext = pRight;
    }
    else if(pNode->m_pParent != nullptr)
    {
        BinaryTreeNode* pCurrent = pNode;
        BinaryTreeNode* pParent = pNode->m_pParent;
        while(pParent != nullptr && pCurrent == pParent->m_pRight)
        {
            pCurrent = pParent;
            pParent = pParent->m_pParent;
        }
        pNext = pParent;
    }
    return pNext;
}
// ==================== 辅助代码用来构建二叉树 ====================
BinaryTreeNode* CreateBinaryTreeNode(int value)
{
    BinaryTreeNode* pNode = new BinaryTreeNode();
    pNode->m_nValue = value;
    pNode->m_pLeft = nullptr;
    pNode->m_pRight = nullptr;
    pNode->m_pParent = nullptr;
    return pNode;
}

void ConnectTreeNodes(BinaryTreeNode* pParent, BinaryTreeNode* pLeft, BinaryTreeNode* pRight)
{
    if(pParent != nullptr)
    {
        pParent->m_pLeft = pLeft;
        pParent->m_pRight = pRight;
        if(pLeft != nullptr)
            pLeft->m_pParent = pParent;
        if(pRight != nullptr)
            pRight->m_pParent = pParent;
    }
}

void PrintTreeNode(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 null.\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 null.\n");
    }
    else
    {
        printf("this node is null.\n");
    }
    printf("\n");
}

void PrintTree(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);
    }
}

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);
    }
}
int main(int argc, char* argv[])
{
    Test1_7();
    Test8_11();
    Test12_15();
    Test16();
}