leetcode 429. N-ary Tree Level Order Traversal（N叉树分层遍历）

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]]

N分支树的level遍历

思路：
BFS

    public List<List<Integer>> levelOrder(Node root) {
        List<List<Integer>> result = new ArrayList<>();
        if(root == null) return result;
        Queue<Node> queue = new LinkedList<>();
        queue.offer(root);
        
        while(!queue.isEmpty()) {
            int size = queue.size();
            List<Integer> tmp = new ArrayList<>();
            for(int i = 0; i < size; i++) {
                Node node = queue.poll();
                tmp.add(node.val);
                for(Node child : node.children) {
                    if(child != null) {
                        queue.offer(child);
                    }
                }
            }
            result.add(tmp);
        }
        return result;
    }