《剑指offer》第五十五题I：二叉树的深度

// 面试题55（一）：二叉树的深度
// 题目：输入一棵二叉树的根结点，求该树的深度。从根结点到叶结点依次经过的
// 结点（含根、叶结点）形成树的一条路径，最长路径的长度为树的深度。

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

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

    int left = TreeDepth(pRoot->m_pLeft);
    int right = TreeDepth(pRoot->m_pRight);

    return (left > right) ? left + 1 : right + 1;
}

// ====================测试代码====================
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);
}

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

    DestroyTree(pNode1);
}

// 树中没有结点
void Test5()
{
    Test("Test5", nullptr, 0);
}

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

    return 0;
}

分析：代码真简洁。

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
class Solution {
public:
    int TreeDepth(TreeNode* pRoot)
    {
        if (pRoot == nullptr)
            return 0;
        
        int left = TreeDepth(pRoot->left);
        int right = TreeDepth(pRoot->right);
        
        return (left > right) ? left + 1 : right + 1;
    }
};