Is Undefined to Null easy or hard?

The problem is rated Medium because it requires careful handling of multiple data types and nested structures. The traversal logic is straightforward, but correctly distinguishing primitives, arrays, and objects is the key challenge.

Undefined to Null Python/Java solution

The core idea remains the same across languages: recursively traverse dictionaries/maps and lists/arrays, replacing undefined-like values with null or None. JavaScript and TypeScript implementations are most common because the problem originates from JavaScript semantics.

How to solve Undefined to Null in O(n)?

Traverse the structure using recursion or a stack. When encountering undefined, return null. If the value is an array or object, iterate through its elements or keys and recursively process each child. Since each node is visited once, the overall complexity remains O(n).

What is the best approach for Undefined to Null?

The most efficient approach is a recursive depth-first traversal of the object or array. Each value is inspected once, and undefined values are replaced with null while traversing nested structures. This solution runs in O(n) time and O(h) space, where h is the maximum nesting depth.

Is Undefined to Null asked at Google/Amazon/Meta?

Problems involving recursive traversal of nested objects or JSON-like structures appear in frontend and JavaScript-focused interviews at companies like Google, Amazon, and Meta. The question tests understanding of recursion, object iteration, and data normalization.

What data structure is used in Undefined to Null?

The solution primarily relies on recursive traversal of JavaScript objects and arrays. Conceptually it behaves like a depth-first search over a tree-like structure where each property or element acts as a node.

What is the time complexity of Undefined to Null?

The time complexity is O(n) because every element, object property, or array entry in the structure is visited exactly once during traversal. Space complexity is O(h) with recursion, where h represents the nesting depth of the structure.

Description Solution Video 3:45

2775. Undefined to Null

Medium69.6% acceptancePremium elsewhere, free here

Given a deeply nested object or array obj, return the object obj with any undefined values replaced by null.

undefined values are handled differently than null values when objects are converted to a JSON string using JSON.stringify(). This function helps ensure serialized data is free of unexpected errors.

Example 1:

Input: obj = {"a": undefined, "b": 3}
Output: {"a": null, "b": 3}
Explanation: The value for obj.a has been changed from undefined to null

Example 2:

Input: obj = {"a": undefined, "b": ["a", undefined]}
Output: {"a": null,"b": ["a", null]}
Explanation: The values for obj.a and obj.b[1] have been changed from undefined to null

Constraints:

obj is a valid JSON object or array
2 <= JSON.stringify(obj).length <= 10⁵

3:45

Still stuck?Read the written solution, or watch a walkthrough.

Open solution

LanguageLoading editor…

1class Solution:
  def solve(self):
      pass


Starter codePython 3Spaces: 4

Examples

Case 1Case 2

Input

{"a": undefined, "b":3}

Input

{"a": undefined, "b":["a", undefined]}

Your code is saved on this device.Solution