C++用层次遍历输出二叉树从根节点到叶子结点的路径

以下是C++代码实现：

#include <iostream>
#include <queue>
#include <vector>

using namespace std;

// 二叉树节点的定义
struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

// 从根节点到叶子结点的路径
vector<vector<int>> binaryTreePaths(TreeNode* root) {
    vector<vector<int>> paths;
    if (!root) {
        return paths;
    }
    queue<TreeNode*> nodeQueue;
    queue<vector<int>> pathQueue;
    nodeQueue.push(root);
    pathQueue.push(vector<int>{root->val});
    while (!nodeQueue.empty()) {
        TreeNode* node = nodeQueue.front();
        vector<int> path = pathQueue.front();
        nodeQueue.pop();
        pathQueue.pop();
        if (!node->left && !node->right) {
            paths.push_back(path);
        } else {
            if (node->left) {
                nodeQueue.push(node->left);
                vector<int> newPath = path;
                newPath.push_back(node->left->val);
                pathQueue.push(newPath);
            }
            if (node->right) {
                nodeQueue.push(node->right);
                vector<int> newPath = path;
                newPath.push_back(node->right->val);
                pathQueue.push(newPath);
            }
        }
    }
    return paths;
}

int main() {
    // 构造二叉树
    TreeNode* root = new TreeNode(1);
    root->left = new TreeNode(2);
    root->right = new TreeNode(3);
    root->left->right = new TreeNode(5);
    root->right->left = new TreeNode(4);

    // 输出从根节点到叶子结点的路径
    vector<vector<int>> paths = binaryTreePaths(root);
    for (auto path : paths) {
        for (auto node : path) {
            cout << node << " ";
        }
        cout << endl;
    }

    return 0;
}

输出结果为：

1 2 5 
1 3 4 

其中，每一行都是从根节点到叶子结点的一条路径。