China's open source AI beats OpenAI

Welcome back!

Amazon loves this week’s problem. Hope you enjoy the challenge!

Here’s what to expect today:

• Longest substring without repeating characters

• Why use Kafka?

Read time: under 4 minutes

CODING CHALLENGE

Longest Substring Without Repeating Characters

Given a string s, find the length of the longest substring without repeating characters.

Example 1:

Input: s = "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.

Example 2:

Input: s = "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: s = "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.

Solve the problem here before reading the solution.

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SOLUTION

To solve this problem, we'll use a sliding window approach with a dictionary. We'll keep track of the characters we've seen and their indices.

We'll move the right pointer of our window, adding characters to the dictionary. If we find a repeating character, we'll move the left pointer to the right of the last occurrence of that character.

We'll update the maximum length of the substring as we go.

The time complexity of this solution is O(n), where n is the length of the input string.

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SYSTEM DESIGN

Why Use Kafka?

Apache Kafka is a distributed data streaming platform designed for high-throughput, real-time data processing. It is used to handle continuous streams of data from many different sources at the same time.

Key features of Kafka:

1. Scalability: Kafka distributes data across multiple servers, allowing it to handle massive amounts of information beyond a single machine's capacity.

2. Speed: With its decoupled write and read data streams, Kafka offers extremely low latency, making it ideal for real-time applications.

3. Durability: Data is replicated across servers and written to disk, protecting against server failures.

4. Flexible data retention: Kafka can store data for configurable periods, from seconds to years.

5. Multiple consumer support: Unlike traditional message queues, Kafka allows multiple applications to read the same data stream independently.

Kafka's architecture combines messaging queue and publish-subscribe models. It organizes data into topics that are partitioned. The messages within a partition are processed in order.

Kafka is used to build real time data pipelines. For example, Uber drivers send their location to the server every few seconds. This location is added to a Kafka queue. From the queue, the location is read by different consumers for applications like matching drivers with riders or showing nearby drivers to the riders on the app.

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NEWS

This Week in the Tech World

Chinese Labs Ship Open Models: Moonshot released Kimi K2.7 Code while Zhipu shipped GLM-5.2, which offers a one million token context window for long autonomous coding, keeping China's open source push squarely in the AI race.

SpaceX Stages Record IPO: SpaceX priced shares at $135 and raised $75 billion, the biggest IPO ever, valuing Elon Musk's rocket maker near $1.75 trillion. Shares listed on the Nasdaq as SPCX and closed up 19 percent on debut.

SpaceX Snaps Up Cursor: Fresh off its blockbuster listing, SpaceX agreed to buy AI coding startup Cursor for $60 billion, its largest acquisition yet. SpaceX shares jumped about 16 percent on the news, lifting its market cap past Amazon and Microsoft.

Bezos Startup Lands $12B: Prometheus, the AI engineering and manufacturing startup co-led by Jeff Bezos, raised $12 billion in Series B at a roughly $41 billion valuation. Backers include JPMorgan, BlackRock, Goldman Sachs, DST Global and Arch Venture Partners.

Mistral Eyes €3B Raise: France's Mistral AI is in talks to raise about €3 billion from venture syndicates and sovereign wealth funds, a deal that would roughly double its valuation to €20 billion and cement its place among Europe's most valuable startups.

Nuvei to Buy Payoneer: Payments firm Nuvei agreed to acquire cross border payments company Payoneer in a $2.75 billion all cash deal, expanding its reach in global business payments.

ServiceNow Trims Hundreds: Enterprise software maker ServiceNow cut hundreds of jobs as it leans harder into automation, joining a wave of profitable tech firms reducing headcount to redirect spending toward AI.

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