视源

1、给定一个二叉树的根节点，返回中序遍历（不用递归）
#include <iostream>
#include <vector>
#include <stack>

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

// 中序遍历的迭代函数
std::vector<int> inorderTraversalIterative(TreeNode* root) {
    std::vector<int> result;
    std::stack<TreeNode*> stack;
    TreeNode* current = root;

    while (current != nullptr || !stack.empty()) {
        while (current != nullptr) {
            stack.push(current);
            current = current->left;
        }
        current = stack.top();
        stack.pop();
        result.push_back(current->val);
        current = current->right;
    }

    return result;
}

int main() {
    // 构建一个简单的二叉树
    // 1
    // / \
    // 2 3
    // / \
    // 4 5
    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);

    // 进行中序遍历
    std::vector<int> result = inorderTraversalIterative(root);
    for (int val : result) {
        std::cout << val << " ";
    }
    return 0;
}
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