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MEDIUMArray, Math, Two PointersThe problem gives an array nums and an integer k. The task is to rotate the
array to the right by k positions, modifying the original list in place.
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MEDIUMDepth-First Search, Breadth-First Search, Graph Theory, Topological SortThere are numCourses courses labeled from 0 to numCourses - 1.
Each prerequisite pair [a, b] means course b must be finished before course a.
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MEDIUMArray, Backtracking, Bit ManipulationGiven an array nums of distinct integers, return every possible subset of those numbers.
A subset can contain none of the numbers, some of the numbers, or all of the numbers. The empty subset [] is valid, and the full array is valid too. Because the input numbers are distinct, there is no duplicate-handling problem in the base version.
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This article turns one of special relativity’s strangest visual predictions into something researchers could finally see in the lab. The subject is the Terrell-Penrose effect, a result that sounds wrong the first time it is described: an object moving close to the speed of light should not simply look squashed in the direction of motion, even though relativity says its length is contracted. To an observer, it should instead look rotated.
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Selected problem: API Rate Limiter
Scope: Design a distributed server-side rate limiter that enforces per-user, per-IP, per-tenant, and per-route API quotas with very low decision latency across many stateless services.
This is the classic server-side API rate limiter from Grokking and Alex Xu: every request should get a cheap admission decision before it reaches expensive application logic.
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Selected problem: Distributed Cache
Scope: Design a distributed in-memory cache service that provides very low-latency GET/SET/DELETE/INCR operations with TTLs, eviction, sharding, and failover for many stateless application services.
This is the classic “design Memcache / Redis-class cache” interview problem: build a shared cache tier that is much faster than the system of record, scales horizontally, and fails gracefully instead of turning into a new bottleneck.
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Selected problem: Notification System
Scope: Design a soft real-time notification platform that accepts events from internal services, renders user-facing messages, respects user preferences, and dispatches push, email, SMS, and in-app notifications reliably at large scale.
Also see https://wiki.derricklin.net/software-development/System%20Design%20Interview/#notification-system
This is the classic “design a notification system” interview problem: build the shared infrastructure that product teams use whenever they need to notify users about security alerts, messages, payments, delivery updates, marketing campaigns, or feed changes. The core challenge is not just calling APNs, FCM, an SMS gateway, or an email provider. The harder parts are durable intake, preference filtering, fanout, queue isolation, retries, deduplication, rate limiting, observability, and honest delivery semantics.
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Techmeme surfaced this April 22, 2026 story in its Techmeme item, and the original article is OpenAI’s Making ChatGPT better for clinicians.
OpenAI is moving ChatGPT more directly into clinical work with a new product called ChatGPT for Clinicians. The product is designed for tasks like documentation, medical research, care consults, referral letters, prior authorization support, and patient instructions. It is initially free for verified individual clinicians in the United States, including physicians, nurse practitioners, physician assistants, and pharmacists.
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This summary covers The Economist’s April 11th, 2026 Business article listed in the contents as A dangerous new AI and published under the headline Mythical monster.
The article argues that warnings about AI danger are usually worth treating with skepticism, because frontier labs have incentives to dramatise their own progress. This time, though, The Economist thinks the warning may be genuine. Its focus is Anthropic’s latest model, Mythos, which the company says is powerful enough at discovering and exploiting software flaws that it should not yet be released broadly.
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Carl Weiseth’s article starts as a behind-the-scenes look at the speedriding film “L’Experience Magnifique,” but its real subject is the hidden infrastructure required to make spectacular mountain footage possible. The finished images may look effortless: tiny wings cutting down steep alpine faces, drone shots threading through gullies, skiers and pilots moving as if the mountain were an open playground. Weiseth makes clear that none of that ease is real. Every successful run depends on planning, communication, weather judgment, transport improvisation, and a group of people who understand that small mistakes in this environment can compound very fast.
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