C++非递归前序遍历二叉树并打印

C++非递归前序遍历二叉树的代码如下：

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

// Definition for a binary tree node.
struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

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

int main() {
    // Create a binary tree
    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);

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

    return 0;
}

非递归前序遍历二叉树的思路是使用栈来模拟递归过程。我们首先把根节点入栈，然后在循环中不断取出栈顶元素，输出它的值，并依次把其右子节点和左子节点入栈。由于栈是后进先出的数据结构，所以先入栈右子节点再入栈左子节点可以保证左子节点先被访问。