Leetcode 429 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, 10^4]

队列 + BFS

和leetcode 102 相同的做法.

/*
// 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>> llist = new ArrayList<>();
        if(root == null)
            return llist;
        Queue<Node> q = new ArrayDeque<>();
        q.offer(root);
        while(!q.isEmpty())
        {
            int size = q.size();
            List<Integer> list = new ArrayList<>();
            while(size != 0)
            {
                Node tmp = q.poll();
                list.add(tmp.val);
                for(Node node : tmp.children)
                {
                    if(node != null)
                        q.offer(node);
                }
                --size;
            }
            llist.add(list);
        }
        return llist;
    }
}