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Quick facts

• Difficulty: MEDIUM
• Problem: Coin Change
• Main tags: Array, Dynamic Programming, Breadth-First Search

What the problem is really asking

The input gives a set of coin denominations and a target amount. Each coin can be used as many times as needed.

The goal is not to count how many different ways the amount can be formed. The goal is to find the fewest coins needed to reach the exact amount. If the amount cannot be formed exactly, the answer is -1.

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What this article is really about

Richard Panek uses cosmology as a case study in scientific humility. The article’s main claim is that astronomy repeatedly treats some picture of the universe as obviously true, only to discover later that the “obvious” picture was built on hidden assumptions.

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Selected problem: ChatGPT

Scope: Design a text-first ChatGPT-style assistant that supports multi-turn conversations, streamed responses, document-backed answers, bounded tool use, and durable conversation history for consumers and teams.

Problem framing

This interview problem combines ideas from several classic designs instead of mapping neatly to one old chapter. Grokking’s framework still applies: clarify scope, define APIs, estimate scale, pick a data model, then explain the high-level design and bottlenecks. Alex Xu’s chat-system chapter is useful for session handling, streaming delivery, and multi-device conversation sync; the YouTube chapter is useful for large-object storage and asynchronous processing; DDIA adds the deeper foundation for logs, caches, replication, partitioning, derived data, and backpressure. The key modern shift is that the assistant is not only a chat transport problem. It is a stateful product sitting on top of an expensive inference pipeline.

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What this article is about

This summary covers The Economist’s April 11th, 2026 By Invitation essay listed in the contents as Sir Nick Clegg on how to catch up in the tech race and published under the headline How Britain and the EU can work together to avoid being lapped in the global tech race.

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Why the phrase can be dangerous

Honza Rejmanek’s article takes a familiar saying and treats it as a serious weather question. Pilots often hear that storms are preceded by a strange lull, but the article argues that the phrase is only partly true and can become dangerous when it is treated as a comforting rule instead of a warning sign. For free-flight pilots, the important question is not whether calm air sometimes appears before a storm, but why it happens and what kind of storm is being discussed.

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JetBlue sued over claims it uses customers’ personal data to set ticket prices (r/news)

• DreamsiclesPlz: Surveillance pricing should be illegal and heavily punished. The US desperately needs better consumer protections. Among a trillion other things…

• Honeycove91: Hey guys, can you remind me what stage of capitalism this is again?

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I JUST joined a startup and I think I’m going to get laid off in the next month (Blind)

• ypfy87 (Amazon): If you got two offers in this market then you can get another. If you feel the axe coming, use your interview momentum to try and get another offer before you get laid off.

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A ski race presented as a ritual instead of a result

Tom Hallberg’s “Collective Effervescence” starts by reframing the Grand Traverse before the race even begins. Father Tim Clark’s annual “Blessing of the Freeheelers” at the starting line makes the event feel less like a standard endurance competition and more like a winter rite, complete with midnight gathering, formal words, and a group of people willingly stepping into discomfort together. Hallberg leans into the absurd facts of the race - roughly 40 miles from Crested Butte to Aspen, 7,000 feet of climbing, heavy packs, frozen water, darkness, altitude, exhaustion - but he does not use them to glorify suffering for its own sake. Instead, he shows how that shared ordeal creates the conditions for a rare kind of meaning.

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Quick facts

• Difficulty: HARD
• Problem: Sliding Window Maximum
• Main tags: Array, Queue, Sliding Window, Heap (Priority Queue), Monotonic Queue

What the problem is really asking

The input gives an array and a window size k. Imagine placing a length-k window over the first k elements, recording the maximum value inside that window, then moving the window one step to the right and repeating until the end.

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Quick facts

• Difficulty: MEDIUM
• Problem: Max Consecutive Ones III
• Main tags: Array, Binary Search, Sliding Window, Prefix Sum

What the problem is really asking

This problem sounds like a bit-flipping question, but the useful reframe is simpler:

find the longest contiguous subarray that contains at most k zeroes.