请用C++和class实现二叉树前序、中序、后序遍历的递归算法

C语言实现二叉树遍历的递归算法：

#include <stdio.h>
#include <stdlib.h>

// 定义二叉树节点
typedef struct TreeNode {
    int val;
    struct TreeNode* left;
    struct TreeNode* right;
} TreeNode;

// 创建二叉树
TreeNode* createTree() {
    TreeNode* root = (TreeNode*) malloc(sizeof(TreeNode));
    root->val = 1;
    root->left = (TreeNode*) malloc(sizeof(TreeNode));
    root->left->val = 2;
    root->left->left = (TreeNode*) malloc(sizeof(TreeNode));
    root->left->left->val = 4;
    root->left->left->left = NULL;
    root->left->left->right = NULL;
    root->left->right = (TreeNode*) malloc(sizeof(TreeNode));
    root->left->right->val = 5;
    root->left->right->left = NULL;
    root->left->right->right = NULL;
    root->right = (TreeNode*) malloc(sizeof(TreeNode));
    root->right->val = 3;
    root->right->left = (TreeNode*) malloc(sizeof(TreeNode));
    root->right->left->val = 6;
    root->right->left->left = NULL;
    root->right->left->right = NULL;
    root->right->right = (TreeNode*) malloc(sizeof(TreeNode));
    root->right->right->val = 7;
    root->right->right->left = NULL;
    root->right->right->right = NULL;
    return root;
}

// 前序遍历
void preOrder(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    printf("%d ", root->val);
    preOrder(root->left);
    preOrder(root->right);
}

// 中序遍历
void inOrder(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    inOrder(root->left);
    printf("%d ", root->val);
    inOrder(root->right);
}

// 后序遍历
void postOrder(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    postOrder(root->left);
    postOrder(root->right);
    printf("%d ", root->val);
}

int main() {
    TreeNode* root = createTree();
    printf("前序遍历结果：");
    preOrder(root);
    printf("\n中序遍历结果：");
    inOrder(root);
    printf("\n后序遍历结果：");
    postOrder(root);
    printf("\n");
    return 0;
}

使用class实现二叉树遍历的递归算法：

#include <iostream>

using namespace std;

// 定义二叉树节点
class TreeNode {
public:
    int val;
    TreeNode* left;
    TreeNode* right;

    TreeNode(int val) {
        this->val = val;
        this->left = NULL;
        this->right = NULL;
    }
};

// 创建二叉树
TreeNode* createTree() {
    TreeNode* root = new TreeNode(1);
    root->left = new TreeNode(2);
    root->left->left = new TreeNode(4);
    root->left->right = new TreeNode(5);
    root->right = new TreeNode(3);
    root->right->left = new TreeNode(6);
    root->right->right = new TreeNode(7);
    return root;
}

// 前序遍历
void preOrder(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    cout << root->val << " ";
    preOrder(root->left);
    preOrder(root->right);
}

// 中序遍历
void inOrder(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    inOrder(root->left);
    cout << root->val << " ";
    inOrder(root->right);
}

// 后序遍历
void postOrder(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    postOrder(root->left);
    postOrder(root->right);
    cout << root->val << " ";
}

int main() {
    TreeNode* root = createTree();
    cout << "前序遍历结果：";
    preOrder(root);
    cout << endl << "中序遍历结果：";
    inOrder(root);
    cout << endl << "后序遍历结果：";
    postOrder(root);
    cout << endl;
    return 0;
}