429. N-ary Tree Level Order Traversal

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

1. Use recursion:

//44 ms    11.7 MB
/*
// 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:
    vector<vector<int>> levelOrder(Node* root) {
        vector<vector<int>> result;
        preorder(root, result, 1);
        return result;
    }
private:
    void preorder(Node* root, vector<vector<int>>& result, int distance) {
        if(!root) return;
        //push vector<int> in a vector
        while(result.size() < distance)
            result.push_back({});
        result[distance-1].push_back(root->val);
        //auto element is a simple way to go around this set
        for(auto child: root->children)
            preorder(child, result, distance + 1);
    }
};