The Ultimate Questions List appeared on multiple platforms

Arrays, Strings & Two Pointers

• Find Longest Duplicated Substring: Find the longest contiguous sequence of characters that appears more than once in a string. (Difficulty: Level 4)
• Minimum Covering Substring: Find the shortest substring of s that contains every character of t. (Difficulty: Level 1)
• Dictionary Substring Check: Verify if every contiguous substring of a given string is a valid word in a provided dictionary. (Difficulty: Level 3)
• Prefix Duplicates Removal: Delete elements from listB so that its first k elements share no value with listA. (Difficulty: Level 5)
• Range Overwrite Queries: Apply a list of (left, right, value) overwrite queries to an integer array. (Difficulty: Level 2)
• Alternating Parity Subarrays: Answer range queries to determine if a subarray has strictly alternating even and odd parities. (Difficulty: Level 4)
• Largest Digit-Sharing Subset: From a list of two-digit integers, find the largest subset where every integer shares at least one digit with another. (Difficulty: Level 1)
• Median of RLE Arrays: Find the median of two run-length encoded (RLE) arrays sorted by value. (Difficulty: Level 5)
• Green-Only Wordle: Choose optimal guesses from a dictionary to find a hidden 5-letter word using only exact-match feedback. (Difficulty: Level 3)
• Decompress Nested Repeats: Decompress an encoded string where parentheses denote groups and numbers dictate repetition counts. (Difficulty: Level 2)

Graphs, Trees & Matrix Traversal

• Minimax Grid Path: Minimize the maximum terrain height you must traverse to get from the top-left to the bottom-right of a grid. (Difficulty: Level 5)
• Distance to Nearest Taxi: In a grid map, compute the distance from every empty cell to the nearest taxi. (Difficulty: Level 2)
• Shortest Path with Blockers: Compute the shortest distance between two nodes in an unweighted graph, avoiding a specific list of blocked nodes. (Difficulty: Level 1)
• Distance-Sum from Tree Nodes: In an undirected, cycle-free tree, compute the sum of distances from each node to all other nodes. (Difficulty: Level 4)
• Chicken Genealogy (LCA): Given parent-child relationships, determine if two specific nodes (chickens) are related. (Difficulty: Level 3)
• Course Catalog Dependencies: Validate an e-learning course catalog given a set of courses and prerequisite pairs (detect cycles/topological sort). (Difficulty: Level 2)
• Trinary Tree Mode: Find the most frequently occurring value in a search tree where nodes can have up to three children. (Difficulty: Level 5)
• Movie Recommendation Graph: Recommend top movies based on a set of movies and an undirected similarity graph. (Difficulty: Level 1)
• Connected Crop Layout: Construct a garden grid planted with k crops, ensuring all regions are connected and safe paths exist. (Difficulty: Level 4)

Intervals & Scheduling

• Minimum Rooms Needed: Calculate the absolute minimum number of meeting rooms required to accommodate a list of overlapping meeting intervals. (Difficulty: Level 3)
• Servers for Cyclic Tasks: Compute the minimum servers needed to run a list of repeating/cyclic tasks represented by (start, duration). (Difficulty: Level 5)
• Circular Day Meetings: Calculate minimum meeting rooms for intervals scheduled within a 24-hour cyclic day (where 23:59 wraps to 00:00). (Difficulty: Level 1)
• Safe Space Travel: Find safe travel intervals along an x-axis given a list of planets and their coordinates/zones of influence. (Difficulty: Level 4)
• Assign Meetings with Delays: Assign meetings to a fixed number of rooms while factoring in dynamic delays. (Difficulty: Level 2)

Dynamic Programming, Greedy & Optimization

• Tokens & Coins Board Game: Maximize coins collected on a 1D board where tokens can only jump exactly 3 steps. (Difficulty: Level 4)
• Bounded Knapsack DP: Solve a variation of the knapsack problem and reconstruct the optimal set of chosen items. (Difficulty: Level 1)
• Non-Adjacent Sum (House Robber): Maximize the sum of a subset of an array such that no two selected indices are adjacent. (Difficulty: Level 3)
• Winning Mahjong Hand: Determine if a 14-tile integer array represents a valid winning configuration. (Difficulty: Level 5)
• Delivery Route with Danger: Compute the shortest delivery route across stops, factoring in specific nodes marked as dangerous. (Difficulty: Level 2)

System Design & Architecture

• O(1) Random Access Set: Design a "FancySet" that supports adding, removing, and returning a random element in average O(1) time. (Difficulty: Level 4)
• Stream K-th Largest: Design a class to track the k-th largest element as a continuous stream of numbers arrives. (Difficulty: Level 1)
• Multi-Type Server Allocation: Design a service to manage 100,000 server nodes where clients request specific instance types. (Difficulty: Level 5)
• Top-K Logger: Design an in-memory logger that records events and can efficiently query the top K most frequent messages. (Difficulty: Level 2)
• Elevator Control System: Design software for a multi-elevator system in a high-rise, including scheduling and car assignment. (Difficulty: Level 3)
• Autocomplete Trie: Implement a service using a prefix tree that supports insert, update, and delete with word weights. (Difficulty: Level 4)

Data Science, Math & Probability

• 1D Dice Walk Probability: Compute the probability of landing on a specific target when repeatedly rolling a 1-to-K fair die on an infinite number line. (Difficulty: Level 3)
• Simulate Uniform(0,1): Use a provided rand_bit() function (returns 0 or 1) to generate a random float uniformly distributed between 0 and 1. (Difficulty: Level 5)
• Invoice Reconciliation: Build an algorithm to match a list of invoice records to payments based on memo text or exact amounts. (Difficulty: Level 1)
• Imbalanced Precision-Recall: Compute evaluation metrics and a PR curve for a highly imbalanced dataset (5% positive rate). (Difficulty: Level 4)
• Two Sum-of-Squares: Find all integers $s<n$ that can be expressed as a sum of two squares in exactly two distinct unique ways. (Difficulty: Level 2)
• Bootstrap Percentage RMSE: Implement a function to calculate pRMSE and compute its confidence interval using bootstrapping. (Difficulty: Level 3)
• Next-Word Predictor: Build an NLP model over tokenized training sentences to predict the next word based on frequencies. (Difficulty: Level 2)