c++编写二叉树前序遍历非递归

下面是C++编写二叉树前序遍历非递归的代码：

#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*> stk;
    stk.push(root);
    while(!stk.empty()) {
        TreeNode* node = stk.top();
        stk.pop();
        cout<<node->val<<" ";
        if(node->right != NULL) {
            stk.push(node->right);
        }
        if(node->left != NULL) {
            stk.push(node->left);
        }
    }
}

int main() {
    // test case
    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<<"preorderTraversal:"<<endl;
    preorderTraversal(root);
    return 0;
}

上面的代码通过使用栈来模拟递归过程，实现了二叉树的前序遍历。