Is N-ary Tree Preorder Traversal easy or hard?

N-ary Tree Preorder Traversal is classified as an easy problem. It mainly tests understanding of preorder traversal and DFS. Once you know the traversal order (node before children), the recursive implementation is short and direct.

N-ary Tree Preorder Traversal Python/Java solution

Python and Java solutions typically implement recursive DFS with a helper function that visits the node and then iterates through its children list. The iterative approach uses a stack (list in Python or Stack/Deque in Java) to simulate the recursion while maintaining preorder order.

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

Use depth-first search. Start at the root, append its value to the result, and recursively process each child in order. An iterative version uses a stack: pop a node, record its value, and push its children in reverse order so the leftmost child is processed first.

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

Recursive depth-first search is the most straightforward approach. Visit the current node, then recursively traverse each child from left to right. It runs in O(n) time because every node is visited once, and uses O(h) space for the recursion stack where h is the tree height.

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

Tree traversal problems appear frequently in interviews at companies like Google, Amazon, and Meta. Variants involving binary trees, N-ary trees, and DFS traversal patterns are commonly used to test understanding of recursion, stacks, and tree data structures.

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

The traversal uses either the call stack through recursion or an explicit stack data structure for the iterative solution. The tree itself stores a list of children for each node, which you iterate through during the DFS process.

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

The time complexity is O(n), where n is the number of nodes in the tree. Each node is visited exactly once during the traversal. Both recursive DFS and iterative stack implementations maintain the same time complexity.

Description Solution Video 6:25

589. N-ary Tree Preorder Traversal

Easy76.7% acceptance2 companies

Given the root of 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)

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 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 2 companies

Google Amazon

Topics

6:25

Still stuck?Read 4 approaches, or watch a walkthrough.

Open solution

589. N-ary Tree Preorder Traversal

Asked at 2 companies

Topics

Similar problems