二叉树的非递归遍历c++

二叉树的非递归遍历可以使用栈来实现。以下是 C++ 实现的代码：

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

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

void preOrderTraversal(TreeNode* root) {
    if (root == NULL) return;
    stack<TreeNode*> s;
    s.push(root);
    while (!s.empty()) {
        TreeNode* cur = s.top();
        s.pop();
        cout << cur->val << " ";
        if (cur->right) s.push(cur->right);
        if (cur->left) s.push(cur->left);
    }
}

void inOrderTraversal(TreeNode* root) {
    if (root == NULL) return;
    stack<TreeNode*> s;
    TreeNode* cur = root;
    while (cur != NULL || !s.empty()) {
        while (cur != NULL) {
            s.push(cur);
            cur = cur->left;
        }
        cur = s.top();
        s.pop();
        cout << cur->val << " ";
        cur = cur->right;
    }
}

void postOrderTraversal(TreeNode* root) {
    if (root == NULL) return;
    stack<TreeNode*> s;
    TreeNode* cur = root;
    TreeNode* last = NULL;
    while (cur != NULL || !s.empty()) {
        while (cur != NULL) {
            s.push(cur);
            cur = cur->left;
        }
        cur = s.top();
        if (cur->right == NULL || cur->right == last) {
            s.pop();
            cout << cur->val << " ";
            last = cur;
            cur = NULL;
        } else {
            cur = cur->right;
        }
    }
}

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;
    return 0;
}

这里实现了三种遍历方式：前序遍历、中序遍历和后序遍历。其中，前序遍历和中序遍历比较简单，后序遍历需要使用一个 `last` 指针来记录上一个被访问的结点，以判断当前结点是否可以被访问。