429. N-ary Tree Level Order Traversal（N叉树的层序遍历）

题目描述

Given an n-ary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).

For example, given a 3-ary tree:

方法思路

class Solution {
    //Runtime: 5 ms, faster than 58.99%
    //Memory Usage: 48.4 MB, less than 48.55% 
    public List<List<Integer>> levelOrder(Node root) {
        List<List<Integer>> ans = new ArrayList<>();
        if(root == null) return ans;
        Queue<Node> queue = new LinkedList<>();
        queue.offer(root);
        List<Integer> l = new ArrayList<>();
        l.add(root.val);
        ans.add(l);
        while(!queue.isEmpty()){
            int size = queue.size();
            while(size-- > 0){
                Node node = queue.poll();
                if(node.children != null)
                    for(Node n : node.children)
                        queue.offer(n);
            }
            if(queue.size() > 0){
                List<Integer> list = new ArrayList<>();
                for(Node node : queue)
                    list.add(node.val);
                ans.add(list);
            }
        }
        return ans;
    }
}