二叉树前中后序遍历c++

以下是二叉树的前中后序遍历的 C++ 代码：

#include <iostream>
#include <stack>

using namespace std;

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

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

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

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

// 非递归前序遍历
void preorderTraversalNonRecursive(TreeNode* root) {
    if (root == NULL) return;
    stack<TreeNode*> s;
    s.push(root);
    while (!s.empty()) {
        TreeNode* curr = s.top();
        s.pop();
        cout << curr->val << " ";
        if (curr->right != NULL) s.push(curr->right);
        if (curr->left != NULL) s.push(curr->left);
    }
}

// 非递归中序遍历
void inorderTraversalNonRecursive(TreeNode* root) {
    if (root == NULL) return;
    stack<TreeNode*> s;
    TreeNode* curr = root;
    while (curr != NULL || !s.empty()) {
        while (curr != NULL) {
            s.push(curr);
            curr = curr->left;
        }
        curr = s.top();
        s.pop();
        cout << curr->val << " ";
        curr = curr->right;
    }
}

// 非递归后序遍历
void postorderTraversalNonRecursive(TreeNode* root) {
    if (root == NULL) return;
    stack<TreeNode*> s1, s2;
    s1.push(root);
    while (!s1.empty()) {
        TreeNode* curr = s1.top();
        s1.pop();
        s2.push(curr);
        if (curr->left != NULL) s1.push(curr->left);
        if (curr->right != NULL) s1.push(curr->right);
    }
    while (!s2.empty()) {
        cout << s2.top()->val << " ";
        s2.pop();
    }
}

int main() {
    TreeNode* root = new TreeNode(1);
    root->left = new TreeNode(2);
    root->right = new TreeNode(3);
    root->left->left = new TreeNode(4);
    root->left->right = new TreeNode(5);
    root->right->left = new TreeNode(6);
    root->right->right = new TreeNode(7);

    cout << "Preorder traversal: ";
    preorderTraversal(root);
    cout << endl;

    cout << "Inorder traversal: ";
    inorderTraversal(root);
    cout << endl;

    cout << "Postorder traversal: ";
    postorderTraversal(root);
    cout << endl;

    cout << "Non-recursive preorder traversal: ";
    preorderTraversalNonRecursive(root);
    cout << endl;

    cout << "Non-recursive inorder traversal: ";
    inorderTraversalNonRecursive(root);
    cout << endl;

    cout << "Non-recursive postorder traversal: ";
    postorderTraversalNonRecursive(root);
    cout << endl;

    return 0;
}

输出结果为：

Preorder traversal: 1 2 4 5 3 6 7 
Inorder traversal: 4 2 5 1 6 3 7 
Postorder traversal: 4 5 2 6 7 3 1 
Non-recursive preorder traversal: 1 2 4 5 3 6 7 
Non-recursive inorder traversal: 4 2 5 1 6 3 7 
Non-recursive postorder traversal: 4 5 2 6 7 3 1