Generated by Codex with GPT-5

Kalshi suspends, fines 3 congressional candidates in ‘insider trading’ enforcement actions (r/news)

• sharrrper: I thought insider trading was suppossed to be a feature of “prediction markets” because it makes the predictions more accurate?

• rubyaeyes: It’s almost like all these financial laws should apply to “predictive” markets too.

  Continue ...

Generated by Codex with GPT-5

Is Meta spying on me? (Blind)

• San-Ti 👾 (Baxter): Bro, Meta’s business model is spying on everyone. You guy’s build spying tool, tracking everyone even those not signed up for meta products.

• jimini (Google): What rock have you been living under? Meta has been spying on everyone for years.

  Continue ...

Generated by Codex with GPT-5

The comforting lie in a tracked slope

Kevin Hjertaas opens “The Tracked Experience” with a contradiction that most backcountry skiers already feel in their bones. Everyone learns the standard warning that tracks do not equal safety. A slope can be skied repeatedly and still avalanche. At the same time, almost everyone also senses that the hundredth skier on a line is not facing exactly the same snowpack as the first. Hjertaas takes that tension seriously instead of smoothing it over. His article is useful because it neither indulges the lazy confidence that comes from seeing old tracks nor falls back on slogans that ignore how snow actually changes under repeated traffic.

Generated by Codex with GPT-5

Quick facts

• Difficulty: HARD
• Problem: Split Array Largest Sum
• Main tags: Array, Binary Search, Dynamic Programming, Greedy, Prefix Sum

What the problem is really asking

The input array must be cut into exactly k non-empty, contiguous pieces. Each cut creates one subarray, and the score of a split is the largest subarray sum that appears anywhere in that split.

Generated by Codex with GPT-5

Quick facts

• Difficulty: MEDIUM
• Problem: Single Element in a Sorted Array
• Main tags: Array, Binary Search

What the problem is really asking

The array is sorted, and every value appears exactly twice except for one value that appears once.

If the array were not sorted, the quickest idea would be XOR: identical values cancel out, so the final XOR is the answer. That works in O(n) time and O(1) space.

Generated by Codex with GPT-5.4

Difficulty: MEDIUM
Problem: Sort an Array

Problem gist

The task is deliberately simple to state: given an integer array, return the same values in ascending order. The interview signal is not whether someone knows Python’s built-in sort, but whether they can implement a sorting strategy with clear time and space guarantees.

Generated by Codex with GPT-5

The Milky Way Is Only “Flat” in the Simplest Sense

Phil Plait’s column takes aim at one of the standard shortcuts in astronomy: the claim that the Milky Way is a flat disk. That description is useful, and it is not exactly wrong, but it leaves out the increasingly strange details that new observations have exposed. The galaxy is indeed a broad disk about 120,000 light-years across, with a dense central bulge and a vast surrounding halo of stars and dark matter. Yet the disk is not a neat, rigid plane. It is bent, twisted and now known to move in ways that look more like a ripple than a sheet of paper.

Generated by Codex with gpt-5

Selected problem: Chat/Messaging System

Scope: Design a text-first chat platform for one-to-one and small-to-medium group conversations with presence, multi-device sync, offline delivery, and durable message history.

Also see https://wiki.derricklin.net/software-development/System%20Design%20Interview/#chat-system

Problem framing

This is the classic interview problem of designing a real-time chat system without over-promising impossible guarantees. Grokking and Alex Xu both frame the core problem similarly: keep message delivery low-latency, keep history durable, handle offline users, and make multiple devices converge on the same conversation state. DDIA adds the deeper constraint: ordering, replication, partitioning, and delivery semantics must be chosen deliberately instead of hand-waving toward “global consistency.”

Generated by Codex with gpt-5

Selected problem: News Feed

Scope: Design a personalized feed service that lets users publish posts, reads recent and ranked posts from accounts they follow, and keeps feed retrieval fast while handling fanout skew, stale caches, media, and eventual consistency.

Also see https://wiki.derricklin.net/software-development/System%20Design%20Interview/#news-feed

Problem framing

This is the classic “design a Facebook News Feed / Twitter timeline / Instagram home feed” interview problem. Grokking and Alex Xu frame it as two linked flows: feed publishing, where a new post enters storage and is propagated to followers, and feed retrieval, where a user gets a fast, paginated, hydrated list of feed items. DDIA’s Twitter home-timeline example explains the central tradeoff: doing more work at write time makes reads fast, but high-follower authors create fanout storms; doing more work at read time avoids write amplification, but every feed read becomes an expensive merge.

Generated by Codex with gpt-5

Selected problem: Search Autocomplete

Scope: Design a low-latency autocomplete service that returns top suggestions for a typed prefix, learns from query activity over time, and handles hot prefixes, moderation, and multilingual growth without rebuilding everything on every keystroke.

Problem framing

This is the classic “design Google search suggestions” or “typeahead” interview problem. Alex Xu frames it around a brutally simple user-facing requirement: every keystroke can trigger a request, so suggestion reads must be extremely fast. Grokking’s interview style also applies cleanly here: clarify prefix-only versus infix matching, top-K size, language scope, freshness needs, and latency targets before arguing about data structures. The interview answer usually starts with a trie or prefix tree, but DDIA adds the more durable framing: autocomplete is a derived read model built from query logs, aggregation, filtering, and ranking pipelines, so the real design question is how to keep that read model fresh, cheap, and rebuildable.