[
     [1],
     [3,2,4],
     [5,6]
]

/*
// Definition for a Node.
class Node {
public:
    int val;
    vector<Node*> children;
​
    Node() {}
​
    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/
class Solution {
public:
    vector<vector<int>> levelOrder(Node* root) {
        deque<Node*> d;
        vector<vector<int>> res;
        if(!root)
            return res;
​
        d.push_back(root);
        while(!d.empty())
        {
            vector<int >tmp;
            for(auto i: d)
                tmp.push_back(i->val);
            int len=d.size();
            while(len--)
            {
                if(d[0]->children.empty())
                    d.pop_front();
                else
                {
​
                    for(auto i: d[0]->children)
                        d.push_back(i);
                    d.pop_front();
                }
            }
            res.push_back(tmp);
​
        }
        return res;
​
    }
};