429. N-ary Tree Level Order Traversal.cpp

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, 104]



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

    Node() {}

    Node(int _val) {
        val = _val;
    }

    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/

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