Is N-ary Tree Postorder Traversal easy or hard?

N-ary Tree Postorder Traversal is considered an easy problem. The main requirement is understanding DFS traversal order and adapting it from binary trees to nodes that may contain multiple children.

N-ary Tree Postorder Traversal Python/Java solution

In Python or Java, implement a DFS function that iterates through node.children and recursively processes each child before appending the node value to a result list. Both languages produce a clean O(n) implementation with minimal code.

How to solve N-ary Tree Postorder Traversal in O(n)?

Use depth-first search to visit every node once. Recursively traverse each child of the current node and append the node value after all children are processed. An iterative version using a stack and reversing the result also achieves O(n) time.

What is the best approach for N-ary Tree Postorder Traversal?

The recursive depth-first search approach is the most common and easiest to implement. Traverse all children of a node first and then add the node value to the result. This directly follows the definition of postorder traversal and runs in O(n) time with O(h) recursion stack space.

Is N-ary Tree Postorder Traversal asked at Google/Amazon/Meta?

Tree traversal problems are common in interviews at companies like Google, Amazon, and Meta. Variations of N-ary tree traversal test understanding of DFS, recursion, and stack-based traversal techniques.

What data structure is used in N-ary Tree Postorder Traversal?

The core structure is an N-ary tree where each node contains a list of children. Implementations typically use recursion (implicit stack) or an explicit stack data structure to perform depth-first traversal.

What is the time complexity of N-ary Tree Postorder Traversal?

The time complexity is O(n) because every node in the tree is visited exactly once. Whether using recursion or an iterative stack, each node is processed a single time during traversal.

Description Solution Video 7:20

590. N-ary Tree Postorder Traversal

Easy81.0% acceptance3 companies

Given the root of an n-ary tree, return the postorder 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: [5,6,3,2,4,1]

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: [2,6,14,11,7,3,12,8,4,13,9,10,5,1]

Constraints:

The number of nodes in the tree is in the range [0, 10⁴].
0 <= Node.val <= 10⁴
The height of the n-ary tree is less than or equal to 1000.

Follow up: Recursive solution is trivial, could you do it iteratively?

Asked at 3 companies

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7:20

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590. N-ary Tree Postorder Traversal

Asked at 3 companies

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