二叉树的层次遍历c++树的方法

以下是C++语言实现二叉树层次遍历的方法：

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

// 定义二叉树结构体
struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

// 层次遍历函数
vector<vector<int>> levelOrder(TreeNode* root) {
    vector<vector<int>> res;
    if (!root) {
        return res;
    }
    queue<TreeNode*> q{{root}};
    while (!q.empty()) {
        vector<int> oneLevel;
        for (int i = q.size(); i > 0; --i) {
            TreeNode* t = q.front(); q.pop();
            oneLevel.push_back(t->val);
            if (t->left) {
                q.push(t->left);
            }
            if (t->right) {
                q.push(t->right);
            }
        }
        res.push_back(oneLevel);
    }
    return res;
}

// 测试
int main() {
    TreeNode* root = new TreeNode(3);
    root->left = new TreeNode(9);
    root->right = new TreeNode(20);
    root->right->left = new TreeNode(15);
    root->right->right = new TreeNode(7);
    vector<vector<int>> res = levelOrder(root);
    for (auto& level : res) {
        for (auto& val : level) {
            cout << val << " ";
        }
        cout << endl;
    }
    return 0;
}