0429. N ary Tree Level Order Traversal - kumaeki/LeetCode GitHub Wiki

0429. 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]

解法1

链表.

/*
// 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>> result = new ArrayList<>();
        if(root == null)
            return result;
        
        ArrayDeque<Node> que = new ArrayDeque<>();
        que.addLast(root);
        while(que.size() > 0){
            List<Integer> list = new ArrayList<>();
            int size = que.size();
            while(size-- > 0){
                Node node = que.removeFirst();
                list.add(node.val);
                node.children.forEach(c -> que.addLast(c));
            }
            result.add(list);
        }
        return result;
    }
}
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