429. N-ary Tree Level Order Traversal

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LeetCode

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Problem

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]]

Code

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

    public Node() {}

    public Node(int _val) {
        val = _val;
    }

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

class Solution {
    public List<List<Integer>> levelOrder(Node root) {
        List<List<Integer>> res = new ArrayList<>();
        if(root == null) return res;

        Queue<Node> queue = new LinkedList<>();
        queue.offer(root);

        while(!queue.isEmpty()) {
            int size = queue.size();
            List<Integer> curr = new ArrayList<>();
            for(int i = 0; i < size; i++) {
                Node node = queue.poll();
                curr.add(node.val);
                for(Node child : node.children) {
                    queue.offer(child);
                }
            }

            res.add(curr);
        }

        return res;
    }
}