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This week’s coding challenge is not as easy as it looks. Even if you know the solution, finding the time complexity is hard. Let’s see if you can solve it.

Today we will cover:

• Convert Sorted Array to Binary Search Tree

• Idempotency in Distributed Systems

Read time: under 4 minutes

CODING CHALLENGE

Convert Sorted Array to Binary Search Tree

Given an integer array nums where the elements are sorted in ascending order, convert it to a height-balanced binary search tree.

Example 1:

Input: nums = [-10,-3,0,5,9]
Output: [0,-3,9,-10,null,5]
Explanation: [0,-10,5,null,-3,null,9] is also accepted:

Example 2:

Input: nums = [1,3]
Output: [3,1]
Explanation: [1,null,3] and [3,1] are both height-balanced BSTs.

Solve the problem here before reading the solution.

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SOLUTION

To convert a sorted array into a height-balanced BST, we can use a recursive approach. The middle element of the array will be the root of our tree. The left subtree will be constructed from elements before the middle element, and the right subtree from elements after the middle element.

The time complexity of this solution is O(n), where n is the number of elements in the array. That’s because we’re processing each element exactly once.

Many people might think that the time complexity should be O(log(n)) because we are splitting the array in half at each step. But if you notice, we are processing both the left and the right half of the array after splitting. This means that we are not cutting the search space in half at each step. So time complexity is not O(log(n)).

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SYSTEM DESIGN

Idempotency in Distributed Systems

In distributed systems, network failures or timeouts can cause operations to be accidentally repeated. For example, when you click "Submit Payment" and get a network error, you might click again because you don’t know if the first payment went through. This can lead to double payments or other unwanted duplicates. Idempotency solves this problem.

An operation is idempotent if running it multiple times has the same effect as running it once. Here's how we implement idempotency in distributed systems:

1. Idempotency Keys: Each request gets a unique ID. When the server receives a request, it first checks if it has seen this ID before. If yes, it returns the cached response instead of processing the request again.

2. Request De-duplication: The server maintains a record of processed request IDs. This record can be stored in the cache. When a new request arrives, the server checks this record before processing.

3. Natural Idempotency: Some operations are naturally idempotent. Setting a user's name to "John" multiple times has the same effect as doing it once. But incrementing a counter isn't idempotent because each operation changes the result.

Here's a comparison of different types of operations:

Implementing idempotency adds complexity but it’s crucial for building reliable distributed systems. It prevents duplicate operations and gives users confidence that retrying failed requests is safe.

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NEWS

This Week in the Tech World

OpenAI Testing Ads in ChatGPT: OpenAI announced it will test ads in free and Go tiers for US users. Ads appear below responses and won't influence answers. A new $8/month Go tier also launched.

Zipline Raises $600M, Valued at $7.6B: Drone delivery startup Zipline raised $600M and will expand to Houston and Phoenix. The company has surpassed 2 million commercial deliveries worldwide.

Deepgram Raises $130M at $1.3B Valuation: Voice AI startup Deepgram raised a Series C led by AVP. The company provides real-time transcription and speech APIs for enterprise applications.

Nvidia Invests in AI Inference Startup: Nvidia joined a funding round in Baseten, an AI startup focused on running models in production. The move signals Nvidia's bet on inference economics.

Xiaomi Cuts Shipment Targets: Xiaomi and Transsion are reducing 2026 shipment targets amid a global memory supply crunch. AI-era demand is pressuring memory and storage supply chains.

Microsoft Patches Windows 11 Bug: Microsoft released an out-of-band fix after a January security update caused shutdown issues on some Windows 11 devices.

Sony Cedes Bravia TV to TCL: Sony is handing control of its Bravia TV brand operations to TCL under a strategic partnership. The move highlights margin pressure in consumer electronics.

UK Eyes Under-16 Social Media Ban: UK ministers are evaluating a model for an under-16 social media ban similar to Australia's, signaling a harder policy turn on youth online safety.

FuriosaAI Seeks $500M Funding: South Korea's FuriosaAI is raising up to $500M ahead of a potential IPO, positioning itself as an Nvidia challenger in the AI accelerator market.

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