如何用c++非递归中序遍历二叉树

以下是C++非递归中序遍历二叉树的代码实现：

#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 inorderTraversal(TreeNode* root) {
    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;
    }
}

int main() {
    TreeNode* root = new TreeNode(1);
    root->right = new TreeNode(2);
    root->right->left = new TreeNode(3);
    inorderTraversal(root); // 输出：1 3 2
    return 0;
}