一、題目

輸入一棵二叉樹的根結點，求該樹的深度。從根結點到葉結點依次經過的結點（含根、葉結點）形成樹的一條路徑，最長路徑的長度為樹的深度。

二、關鍵

三、解釋

四、程式碼

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

int TreeDepth(const BinaryTreeNode* pRoot)
{
    if(pRoot == nullptr)
        return 0;

    int nLeft = TreeDepth(pRoot->m_pLeft);
    int nRight = TreeDepth(pRoot->m_pRight);

    return (nLeft > nRight) ? (nLeft + 1) : (nRight + 1);
}

// ====================測試程式碼====================
void Test(const char* testName, const BinaryTreeNode* pRoot, int expected)
{
    int result = TreeDepth(pRoot);
    if(expected == result)
        printf("%s passed.\n", testName);
    else
        printf("%s FAILED.\n", testName);
}

//            1
//         /      \
//        2        3
//       /\         \
//      4  5         6
//        /
//       7
void Test1()
{
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);
    BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2);
    BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3);
    BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4);
    BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5);
    BinaryTreeNode* pNode6 = CreateBinaryTreeNode(6);
    BinaryTreeNode* pNode7 = CreateBinaryTreeNode(7);

    ConnectTreeNodes(pNode1, pNode2, pNode3);
    ConnectTreeNodes(pNode2, pNode4, pNode5);
    ConnectTreeNodes(pNode3, nullptr, pNode6);
    ConnectTreeNodes(pNode5, pNode7, nullptr);

    Test("Test1", pNode1, 4);

    DestroyTree(pNode1);
}

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

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

    Test("Test2", pNode1, 5);

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

    Test("Test3", pNode1, 5);

    DestroyTree(pNode1);
}

// 樹中只有1個結點
void Test4()
{
    BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1);
    Test("Test4", pNode1, 1);

    DestroyTree(pNode1);
}

// 樹中沒有結點
void Test5()
{
    Test("Test5", nullptr, 0);
}

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

    return 0;
}