Description
https://leetcode.com/problems/n-ary-tree-postorder-traversal/
Given an n-ary tree, return the preorder 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).
Follow up:
Recursive solution is trivial, could you do it iteratively?
Example 1:
Input: root = [1,null,3,2,4,null,5,6] Output: [1,3,5,6,2,4]
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: [1,2,3,6,7,11,14,4,8,12,5,9,13,10]
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]
Explanation
Recursively visit nodes using pre order.
Python Solution
"""
# Definition for a Node.
class Node:
def __init__(self, val=None, children=None):
self.val = val
self.children = children
"""
class Solution:
def preorder(self, root: 'Node') -> List[int]:
results = []
self.helper(root, results)
return results
def helper(self, root, results):
if not root:
return
results.append(root.val)
for child in root.children:
self.helper(child, results)
- Time Complexity: O(N)
- Space Complexity: O(N)