LeetCode: 429. N-ary Tree Level Order Traversal

题目

原题地址:https://leetcode.com/problems/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:

image

Input: root = [1,null,3,2,4,null,5,6]
Output: [[1],[3,2,4],[5,6]]

Example 2:

image2

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

逐层遍历,记下当前层所有节点值然后收集当前层所有节点的子节点作为下一层的节点。

这个方法的 Python 代码类似下面这样:

"""
# Definition for a Node.
class Node(object):
    def __init__(self, val=None, children=None):
        self.val = val
        self.children = children
"""

class Solution(object):
    def levelOrder(self, root):
        if root is None:
            return []

        values = []
        children = [root]

        while children:
            children_values = []
            new_children = []
            for c in children:
                children_values.append(c.val)
                if c.children:
                    new_children.extend(c.children)

            values.append(children_values)
            children = new_children

        return values

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