06. N-ary Tree Level Order Traversal.cpp

/*
N-ary Tree Level Order Traversal
================================

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:
    vector<vector<int>> levelOrder(Node *root)
    {
        vector<vector<int>> ans;
        if (!root)
            return ans;

        queue<Node *> q;
        q.push(root);
        while (q.size())
        {
            vector<int> sub;
            for (int i = q.size(); i > 0; --i)
            {
                auto curr = q.front();
                q.pop();
                sub.push_back(curr->val);
                for (auto &child : curr->children)
                {
                    q.push(child);
                }
            }
            ans.push_back(sub);
        }

        return ans;
    }
};