429. N-ary Tree Level Order Traversal**

429. N-ary Tree Level Order Traversal**

​​https://leetcode.com/problems/n-ary-tree-level-order-traversal/​​

题目描述

Given an n-ary tree, return the level order traversal of its nodes’ values.

Nary-Tree input serialization is represented in their level order traversal, each group of children is separated by the null value (See examples).

Example 1:

Input: root = [1,null,3,2,4,null,5,6]
Output: [[1],[3,2,4],[5,6]]

Example 2:

Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
Output: [[1],[2,3,4,5],[6,7,8,9,10],[11,12,13],[14]]

Constraints:

• The height of the​​n-ary​​ tree is less than or equal to 1000
• The total number of nodes is between​​[0, 10^4]​​

C++ 实现 1

层序遍历使用队列来实现.

/*
// Definition for a Node.
class Node {
public:
    int val;
    vector children;

    Node() {}

    Node(int _val) {
        val = _val;
    }

    Node(int _val, vector _children) {
        val = _val;
        children = _children;
    }
};
*/
class Solution {
public:
    vector<vector<int>> levelOrder(Node* root) {
        if (!root) return {};
        queue<Node*> q;
        q.push(root);
        vector<vector<int>> res;
        while (!q.empty()) {
            auto size = q.size();
            vector<int> tmp;
            while (size --) {
                auto r = q.front();
                q.pop();
                tmp.push_back(r->val);
                for (auto &c : r->children)
                    q.push(c);
            }
            res.push_back(tmp);
        }
        return res;
    }
};