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HARDArray, Hash TableGiven an unsorted integer array, return the smallest positive integer that does not appear in the array.
The tricky part is not the definition of the answer. The tricky part is the constraint: the best solution must run in O(n) time and use only O(1) extra space.
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MEDIUMHash Table, Math, StringThe input is an integer between 1 and 3999, and the output must be its Roman numeral form.
The main challenge is not basic lookup. The hard part is handling the subtractive cases correctly:
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MEDIUMArray, Depth-First Search, Breadth-First Search, Union-Find, MatrixThe board contains X and O. The task is to flip only the O cells that belong to regions fully enclosed by X.
The important phrase is “surrounded region.” A region is safe if it can reach the border through adjacent O cells. A region is captured only if there is no such path.
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MEDIUMArray, Two Pointers, SortingThe input is an integer array and a target value. The job is to pick exactly three numbers whose sum is as close to the target as possible.
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MEDIUMDatabase, SQLThere is an Employee table with a salary column. The task is to return the second-highest distinct salary value.
That word “distinct” is the whole trick.
If the largest salary appears many times, it still counts as only one rank. So this is not:
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MEDIUMLinked List, Two PointersThe input is a singly linked list and a positive integer n.
The task is to delete the node that is n positions from the end and return the new head.
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Yvette Cendes builds the article around one of astronomy’s most dramatic scenes: a star wandering too close to a supermassive black hole. Long before the star crosses the event horizon, gravity pulls much harder on the side nearest the hole than on the far side. The star stretches, unravels and gets torn apart in a tidal disruption event. Roughly half of its material is flung outward, while the rest settles into a hot accretion disk that briefly shines across the universe.
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Techmeme surfaced this story on its April 15, 2026 front page, and the original article is TechCrunch’s After sale of its shoe business, Allbirds pivots to AI.
The basic plot sounds like satire, but it is real. After selling its brand and footwear assets last month for $39 million, Allbirds is using the remaining public-company shell to pivot into AI infrastructure. In its own investor-relations announcement, the company said it signed a $50 million convertible financing facility with an institutional investor, plans to rename itself “NewBird AI,” and wants to become a GPU-as-a-service and AI-native cloud provider.
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This summary covers The Economist’s March 28th, 2026 Science & technology Well Informed article on page 79, which asks whether playing music is good for the brain and answers that it probably is.
The article’s basic point is not that musicians are magical or that music lessons guarantee genius. It is that making music is an unusually demanding mental task. It asks the brain to coordinate hearing, sight, timing, fine motor control, attention and imagination all at once. Done regularly, that seems to act like a form of training that can leave measurable cognitive benefits behind.
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Jeff Katz’s guide is useful because it refuses to romanticize speedriding. The sport is easy to describe in a seductive way: skis, a small wing, steep terrain, and the ability to move between sliding and flying. Katz acknowledges that appeal, but he makes the stronger point that speedriding only stays beautiful when pilots treat it as a discipline rather than a shortcut to intensity. The article is built around progression, judgment, and energy management, not bravado.
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