用C＋＋写二叉树的遍历

二叉树的遍历分为三种：前序遍历、中序遍历和后序遍历。

以下是使用C++实现二叉树遍历的示例代码：

#include <iostream>
#include <stack>

using namespace std;

// 定义二叉树节点
struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
};

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

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

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

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

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

// 非递归后序遍历
void postorderTraversalNonRecursive(TreeNode* root) {
    stack<TreeNode*> s;
    TreeNode* p = root;
    TreeNode* lastVisitedNode = nullptr;
    while (p || !s.empty()) {
        if (p) {
            s.push(p);
            p = p->left;
        } else {
            TreeNode* topNode = s.top();
            if (topNode->right && topNode->right != lastVisitedNode) {
                p = topNode->right;
            } else {
                cout << topNode->val << " ";
                s.pop();
                lastVisitedNode = topNode;
            }
        }
    }
}

int main() {
    // 构建二叉树
    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);

    // 测试遍历算法
    cout << "前序遍历结果：";
    preorderTraversal(root);
    cout << endl;

    cout << "中序遍历结果：";
    inorderTraversal(root);
    cout << endl;

    cout << "后序遍历结果：";
    postorderTraversal(root);
    cout << endl;

    cout << "非递归前序遍历结果：";
    preorderTraversalNonRecursive(root);
    cout << endl;

    cout << "非递归中序遍历结果：";
    inorderTraversalNonRecursive(root);
    cout << endl;

    cout << "非递归后序遍历结果：";
    postorderTraversalNonRecursive(root);
    cout << endl;

    return 0;
}