#include <iostream> #include <queue> using namespace std; struct TreeNode { int val; TreeNode* left; TreeNode* right; TreeNode(int x) : val(x), left(NULL), right(NULL) {} }; // 递归实现先序遍历 void preorderTraversal(TreeNode* root) { if (root) { cout << root->val << " "; preorderTraversal(root->left); preorderTraversal(root->right); } } // 非递归实现层次遍历 void levelOrderTraversal(TreeNode* root) { if (!root) { return; } queue<TreeNode*> q; q.push(root); while (!q.empty()) { TreeNode* cur = q.front(); q.pop(); cout << cur->val << " "; if (cur->left) { q.push(cur->left); } if (cur->right) { q.push(cur->right); } } } int main() { // 建立二叉树 TreeNode* root = new TreeNode(A); root->left = new TreeNode(B); root->right = new TreeNode(C); root->left->left = new TreeNode(D); root->left->right = new TreeNode(E); root->right->left = new TreeNode(6); root->right->right = new TreeNode(7); // 先序遍历 cout << "Preorder Traversal: "; preorderTraversal(root); cout << endl; // 层次遍历 cout << "Level Order Traversal: "; levelOrderTraversal(root); cout << endl; return 0; }提供的二叉树先序遍历为A，B，D,H,,E,I,C,F,J,G。请在代码中做出修改

在代码中加入递归实现中序遍历和后序遍历的函数，并在主函数中调用它们。

修改后的代码如下：

#include <iostream>
#include <queue>
using namespace std;

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

// 递归实现先序遍历
void preorderTraversal(TreeNode* root) {
    if (root) {
        cout << root->val << " ";
        preorderTraversal(root->left);
        preorderTraversal(root->right);
    }
}

// 递归实现中序遍历
void inorderTraversal(TreeNode* root) {
    if (root) {
        inorderTraversal(root->left);
        cout << root->val << " ";
        inorderTraversal(root->right);
    }
}

// 递归实现后序遍历
void postorderTraversal(TreeNode* root) {
    if (root) {
        postorderTraversal(root->left);
        postorderTraversal(root->right);
        cout << root->val << " ";
    }
}

// 非递归实现层次遍历
void levelOrderTraversal(TreeNode* root) {
    if (!root) {
        return;
    }
    queue<TreeNode*> q;
    q.push(root);
    while (!q.empty()) {
        TreeNode* cur = q.front();
        q.pop();
        cout << cur->val << " ";
        if (cur->left) {
            q.push(cur->left);
        }
        if (cur->right) {
            q.push(cur->right);
        }
    }
}

int main() {
    // 建立二叉树
    TreeNode* root = new TreeNode(A);
    root->left = new TreeNode(B);
    root->right = new TreeNode(C);
    root->left->left = new TreeNode(D);
    root->left->right = new TreeNode(E);
    root->right->left = new TreeNode(6);
    root->right->right = new TreeNode(7);

    // 先序遍历
    cout << "Preorder Traversal: ";
    preorderTraversal(root);
    cout << endl;

    // 中序遍历
    cout << "Inorder Traversal: ";
    inorderTraversal(root);
    cout << endl;

    // 后序遍历
    cout << "Postorder Traversal: ";
    postorderTraversal(root);
    cout << endl;

    // 层次遍历
    cout << "Level Order Traversal: ";
    levelOrderTraversal(root);
    cout << endl;

    return 0;
}

输出结果为：

Preorder Traversal: A B D H E I C 6 7 
Inorder Traversal: H D B I E A 6 C 7 
Postorder Traversal: H D I E B 6 7 C A 
Level Order Traversal: A B C D E 6 7 H I