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Quick facts

• Difficulty: HARD
• Problem: N-Queens
• Main tags: Array, Backtracking

What the problem is really asking

The board details can make this problem look more complicated than it is.

At a higher level, the task is:

• place exactly one queen in each row
• never reuse a column
• never place two queens on the same diagonal
• return every full placement that satisfies those rules

That “one queen per row” reframing is the key simplification.

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Quick facts

• Difficulty: MEDIUM
• Problem: House Robber
• Main tags: Array, Dynamic Programming

What the problem is really asking

Each house has some amount of money. The thief wants the largest total possible, but robbing two neighboring houses triggers the alarm.

So the real question is:

At every house, is it better to:

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Quick facts

• Difficulty: MEDIUM
• Problem: Generate Parentheses
• Main tags: String, Dynamic Programming, Backtracking

What the problem is really asking

Given n pairs of parentheses, generate every string that is:

• exactly 2n characters long
• made only of ( and )
• balanced at every point

The last condition is the important one.

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Quick facts

• Difficulty: MEDIUM
• Problem: Search in Rotated Sorted Array
• Main tags: Array, Binary Search

What the problem is really asking

The array started out sorted in ascending order, then got rotated at some pivot.

That means a sequence like [0, 1, 2, 4, 5, 6, 7] might become [4, 5, 6, 7, 0, 1, 2].

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Quick facts

• Difficulty: MEDIUM
• Problem: Find First and Last Position of Element in Sorted Array
• Main tags: Array, Binary Search

What the problem is really asking

The input array is sorted, and the target value may appear many times in one contiguous block.

The task is not just to decide whether the target exists. It is to return the exact starting and ending indices of that block.

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Quick facts

• Difficulty: MEDIUM
• Problem: Group Anagrams
• Main tags: Array, Hash Table, String, Sorting

What the problem is really asking

Two strings belong in the same group if they use the exact same letters with the exact same counts, just in a different order.

So the problem is not really about comparing every string against every other string. It is about finding a stable “signature” for each word, so all words with the same signature land in the same bucket.

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Quick facts

• Difficulty: MEDIUM
• Problem: Spiral Matrix
• Main tags: Array, Matrix, Simulation

What the problem is really asking

The input is a 2D matrix. The task is to return every value exactly once in spiral order:

• go left to right across the top
• then top to bottom down the right side
• then right to left across the bottom
• then bottom to top up the left side
• keep repeating until there is nothing left

This is a traversal problem. Nothing in the matrix needs to be modified. The only challenge is knowing when to turn and when a side has already been fully consumed.

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Quick facts

• Difficulty: MEDIUM
• Problem: Jump Game
• Main tags: Array, Dynamic Programming, Greedy

What the problem is really asking

Each position tells how far the player is allowed to jump from that spot.

The goal is not to find the minimum number of jumps. It is only to decide whether the last index is reachable at all.

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A space rock became a cultural crime scene

Dan Vergano’s article starts with a meteorite that is scientifically extraordinary but locally familiar. Near the Somali village of El Ali, the 13.6-metric-ton iron-and-nickel mass known as Shiid-birood, or “the iron rock,” sat in the landscape for generations. People folded it into stories and songs, chipped bits of iron from it, used it as a whetstone, and treated it less like a museum object than like part of the region’s lived history.

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What happened

Techmeme surfaced this story in its April 11, 2026 roundup, and the original article is Terrence O’Brien’s Google says Polymarket bets showing up in News was an “error”.

The Verge reports that Google News briefly displayed links to Polymarket betting markets alongside coverage from conventional news outlets. One example placed a market about ship traffic through the Strait of Hormuz under search results that also included reporting from outlets like Reuters and The Guardian. Google later removed the results and said Polymarket was not supposed to appear in Google News at all.