Dr. Drang poses a puzzle from the March 2025 issue of Scientific American, involving a square steel plate with a circular hole and a matching square-headed bolt. The challenge is to determine how much the center of the hole moves relative to the plate's center when the bolt is tightened, pulling the head flush against the plate. He outlines his approach using vector analysis, trigonometric identities, and small-angle approximations to derive a simplified solution. He compares this to a purely geometric approach, also presented in the magazine, and finds it both more elegant and more readily generalizable to different hole/head sizes.
The Hacker News post presents a betting game puzzle where you predict the sum of your neighbors' bets, with the closest guess winning. The challenge is to calculate this sum efficiently when dealing with a large number of players, each choosing a bet from 0 to 9. The author shares a clever algorithm that achieves this in linear time, utilizing a frequency array to avoid redundant calculations. This approach significantly improves performance compared to a naive quadratic solution, making the game scalable for a substantial number of participants.
Hacker News users discussed the efficiency and practicality of the presented algorithm for the betting game puzzle. Some questioned the "linear time" claim, pointing out the algorithm's reliance on a precomputed lookup table, the creation of which would not be linear. Others debated the best way to construct such a table efficiently. A few commenters suggested alternative approaches, including using Gray codes or focusing on bit manipulation tricks. There was also discussion about the problem's framing, with some arguing it's more of a dynamic programming exercise than a puzzle. Finally, some users explored variations of the puzzle, such as changing the allowed bet sizes or considering non-integer bets.
Bracket City is a daily online word puzzle that deconstructs the traditional crossword format. Instead of a grid, clues are presented in a bracket-style tournament, where players choose the correct answer from two options to advance. Each correct answer reveals letters that eventually combine to form the final solution word. This unique presentation adds a layer of strategy and deductive reasoning, as incorrect choices don't just leave a gap, but actively lead down the wrong path. The daily puzzle offers a fresh take on wordplay, challenging players to not just know the answers, but also to understand the relationships between them.
Hacker News users discussed the unusual format and difficulty of Bracket City. Several commenters found the puzzle too challenging, describing it as "obtuse" and expressing frustration with the lack of clear instructions or feedback. The unconventional grid and scoring system also drew criticism. Some users questioned the puzzle's description as a crossword, suggesting alternative classifications like a logic puzzle or code-breaking challenge. Despite the difficulty, some commenters expressed intrigue and a desire to understand the solving process better, with one suggesting a walkthrough or tutorial would be helpful. Others appreciated the novelty and different approach to puzzling, even if they found it personally too hard. The puzzle's creator responded to some comments, clarifying certain mechanics and acknowledging the steep learning curve.
Figgie, created by Jane Street, is a trick-taking card game played with a 60-card deck featuring six suits. Players bid on how many tricks they think they can win, with a unique twist: suits are ranked differently each round, adding a layer of strategic complexity. The goal is to accurately predict and achieve your bid, earning points based on successful predictions. The game encourages strategic thinking by requiring players to consider both card strength and the fluctuating suit hierarchy when making bids and playing tricks.
HN commenters discuss Figgie, a card game developed by Jane Street, with some expressing interest in trying it out due to Jane Street's reputation. Several commenters compare it to existing trick-taking games, mentioning similarities to Spades, Bridge, and Hearts. Some express skepticism about the complexity, wondering if it's genuinely intricate or just unnecessarily convoluted. The lack of a physical deck is a point of contention, with some preferring a tangible game experience. Others are intrigued by the strategy and mathematical elements, highlighting the dynamic partnership aspect and the potential for deep analysis. A few commenters note the similarity between "Figgie" and the word "fig," speculating about the name's origin.
SQL Noir is a free, interactive tutorial that teaches SQL syntax and database concepts through a series of crime-solving puzzles. Players progress through a noir-themed storyline by writing SQL queries to interrogate witnesses, analyze clues, and ultimately identify the culprit. The game provides immediate feedback on query correctness and offers hints when needed, making it accessible to beginners while still challenging experienced users with increasingly complex scenarios. It focuses on practical application of SQL skills in a fun and engaging environment.
HN commenters generally expressed enthusiasm for SQL Noir, praising its engaging and gamified approach to learning SQL. Several noted its potential appeal to beginners and those who struggle with traditional learning methods. Some suggested improvements, such as adding more complex queries and scenarios, incorporating different SQL dialects (like PostgreSQL), and offering hints or progressive difficulty levels. A few commenters shared their positive experiences using the platform, highlighting its effectiveness in reinforcing SQL concepts. One commenter mentioned a similar project they had worked on, focusing on learning regular expressions through a detective game. The overall sentiment was positive, with many viewing SQL Noir as a valuable and innovative tool for learning SQL.
SudokuVariants.com lets you play and create a wide variety of Sudoku puzzles beyond the classic 9x9 grid. The website offers different grid sizes, shapes, and rule sets, including variations like Killer Sudoku, Irregular Sudoku, and even custom rule combinations. Users can experiment with existing variants or design their own unique Sudoku challenges using a visual editor, and then share their creations with others via a generated link. The site aims to provide a comprehensive platform for both playing and exploring the vast possibilities within the Sudoku puzzle format.
Hacker News users generally expressed interest in the SudokuVariants website. Several praised its clean design and the variety of puzzles offered. Some found the "construct your own variant" feature particularly appealing, and one user suggested adding a difficulty rating system for user-created puzzles. A few commenters mentioned specific variant recommendations, including "Killer Sudoku" and a variant with prime number constraints. There was also a brief discussion about the underlying logic and algorithms involved in generating and solving these puzzles. One user pointed out that some extreme variants might be NP-complete, implying significant computational challenges for larger grids or complex rules.
Summary of Comments ( 3 )
https://news.ycombinator.com/item?id=43243110
HN users generally found the puzzle trivial, with several pointing out the quick solution of simply measuring the gap between the bolts to determine which one is missing. Some debated the practicality of such a solution, suggesting calipers would be necessary for accuracy, while others argued a visual inspection would suffice. A few commenters explored alternative, more complex approaches involving calculating the center of mass or using image analysis software, but these were generally dismissed as overkill. The discussion also briefly touched on manufacturing tolerances and the real-world implications of such a scenario.
The Hacker News post "A Scientific American bolt puzzle" has generated a modest discussion with several insightful comments focusing primarily on the puzzle's solution and its mathematical underpinnings.
One commenter points out the crucial role of the bolt's thread pitch in determining the relative rotation and linear movement. They explain how a single rotation of the bolt corresponds to a linear advancement equal to the thread pitch. This understanding is fundamental to solving the puzzle, as it clarifies the relationship between the nuts' rotations and their movement along the bolt.
Another commenter delves deeper into the mathematical formalization, introducing the concept of a helix and describing how the nuts' movements can be modeled using parametric equations. This provides a more rigorous and abstract understanding of the problem, moving beyond the intuitive understanding offered by the previous comment. They also suggest a way to visualize the movement of the nuts in 3D space, enhancing the comprehension of the puzzle's dynamics.
Building upon this mathematical approach, another commenter introduces the concept of relative velocity and frames of reference. They explain how considering the movement of one nut relative to the other simplifies the problem and clarifies why both nuts meet in the middle. This perspective shifts the focus from absolute movements to relative motion, making the solution more intuitive.
Several commenters discuss the puzzle's practical implications and how similar principles apply in real-world scenarios like tightening screws. They illustrate how the puzzle's underlying concepts are directly relevant to everyday mechanics.
Finally, one commenter notes the puzzle's resemblance to a classic physics problem involving two trains approaching each other. This analogy provides a simpler, more familiar framework for understanding the relative motion aspect of the puzzle, making it accessible to a broader audience.
Overall, the comments on the Hacker News post offer a range of perspectives on the puzzle, from intuitive explanations to rigorous mathematical formulations and practical applications. They provide a valuable discussion that enhances understanding of the puzzle and its underlying principles.