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Gain exclusive access to our latest and ever-growing collection of premium content, such as questions, Explore cards, and premium solutions, where detailed explanations are written by our team of algorithm and data structure experts.

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~ FAQ ~

What will I get with a premium subscription?

In addition to free questions / articles, you will have access to exclusive premium questions / articles as well. You will also be able to group questions by company, and practice mock interviews targeting a specific company.

What are the premium articles? Is there a sample I can look at?

Some of the articles are reserved for premium subscribers only. You can take a look at this free sample article here. Please note that we are adding more articles so please check back frequently.

How does grouping questions by company work?

We compile the list of questions asked by specific companies based on data from user surveys: "Have you met this question in a real interview?". These lists will be kept up to date frequently with the ever growing survey data. You can find the list of companies in the problem list page, just below the Tag lists.

What about all the existing questions?

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What are the premium questions?   Show

Here is the current up to date premium question list, more is coming...

  1. Fix Names in a Table
  2. Change the Root of a Binary Tree
  3. Average Time of Process per Machine
  4. Correct a Binary Tree
  5. Hopper Company Queries III
  6. Lowest Common Ancestor of a Binary Tree III
  7. Hopper Company Queries II
  8. Lowest Common Ancestor of a Binary Tree II
  9. Hopper Company Queries I
  10. Add Two Polynomials Represented as Linked Lists
  11. Percentage of Users Attended a Contest
  12. Design an Expression Tree With Evaluate Function
  13. All Valid Triplets That Can Represent a Country
  14. Maximum Font to Fit a Sentence in a Screen
  15. Find the Missing IDs
  16. Check If Two Expression Trees are Equivalent
  17. Sellers With No Sales
  18. Find Nearest Right Node in Binary Tree
  19. Build Binary Expression Tree From Infix Expression
  20. The Most Frequently Ordered Products for Each Customer
  21. Bank Account Summary II
  22. Binary Search Tree Iterator II
  23. Customer Who Visited but Did Not Make Any Transactions
  24. Put Boxes Into the Warehouse II
  25. Warehouse Manager
  26. Dot Product of Two Sparse Vectors
  27. Unique Orders and Customers Per Month
  28. Put Boxes Into the Warehouse I
  29. Bank Account Summary
  30. Strings Differ by One Character
  31. The Most Recent Orders for Each Product
  32. The Most Similar Path in a Graph
  33. Fix Product Name Format
  34. Guess the Majority in a Hidden Array
  35. Find the Index of the Large Integer
  36. The Most Recent Three Orders
  37. Patients With a Condition
  38. Diameter of N-Ary Tree
  39. Find Users With Valid E-Mails
  40. Move Sub-Tree of N-Ary Tree
  41. Customer Order Frequency
  42. Find Root of N-Ary Tree
  43. Countries You Can Safely Invest In
  44. Design a File Sharing System
  45. Friendly Movies Streamed Last Month
  46. Clone N-ary Tree
  47. Clone Binary Tree With Random Pointer
  48. Group Sold Products By The Date
  49. Sales by Day of the Week
  50. Delete N Nodes After M Nodes of a Linked List
  51. Find All The Lonely Nodes
  52. Calculate Salaries
  53. Rectangles Area
  54. Active Users
  55. Apples & Oranges
  56. Evaluate Boolean Expression
  57. Create a Session Bar Chart
  58. NPV Queries
  59. Find the Quiet Students in All Exams
  60. Top Travellers
  61. Customers Who Bought Products A and B but Not C
  62. Capital Gain/Loss
  63. Total Sales Amount by Year
  64. Replace Employee ID With The Unique Identifier
  65. Get the Second Most Recent Activity
  66. Number of Trusted Contacts of a Customer
  67. Activity Participants
  68. Students With Invalid Departments
  69. Movie Rating
  70. Number of Transactions per Visit
  71. List the Products Ordered in a Period
  72. Ads Performance
  73. Restaurant Growth
  74. Running Total for Different Genders
  75. Find the Team Size
  76. Check If a String Is a Valid Sequence from Root to Leaves Path in a Binary Tree
  77. Weather Type in Each Country
  78. Find the Start and End Number of Continuous Ranges
  79. Students and Examinations
  80. Traffic Light Controlled Intersection
  81. All People Report to the Given Manager
  82. Print Immutable Linked List in Reverse
  83. Page Recommendations
  84. Counting Elements
  85. Average Selling Price
  86. Web Crawler Multithreaded
  87. Number of Comments per Post
  88. Leftmost Column with at Least a One
  89. Web Crawler
  90. First Unique Number
  91. Report Contiguous Dates
  92. Perform String Shifts
  93. Team Scores in Football Tournament
  94. Queries Quality and Percentage
  95. Monthly Transactions II
  96. Last Person to Fit in the Elevator
  97. Tournament Winners
  98. Monthly Transactions I
  99. Design Bounded Blocking Queue
  100. Immediate Food Delivery II
  101. Immediate Food Delivery I
  102. Diet Plan Performance
  103. Product Price at a Given Date
  104. Market Analysis II
  105. Market Analysis I
  106. Article Views II
  107. Article Views I
  108. User Activity for the Past 30 Days II
  109. User Activity for the Past 30 Days I
  110. Reported Posts II
  111. Number of Ships in a Rectangle
  112. User Purchase Platform
  113. Active Businesses
  114. Reported Posts
  115. Highest Grade For Each Student
  116. Handshakes That Don't Cross
  117. New Users Daily Count
  118. Palindrome Removal
  119. Delete Tree Nodes
  120. Remove Interval
  121. Hexspeak
  122. Unpopular Books
  123. Game Play Analysis V
  124. Divide Chocolate
  125. Synonymous Sentences
  126. Smallest Common Region
  127. Encode Number
  128. Game Play Analysis IV
  129. Game Play Analysis III
  130. Game Play Analysis II
  131. Game Play Analysis I
  132. Valid Palindrome III
  133. Tree Diameter
  134. Design A Leaderboard
  135. Array Transformation
  136. Sales Analysis III
  137. Sales Analysis II
  138. Sales Analysis I
  139. Minimum Time to Build Blocks
  140. Toss Strange Coins
  141. Meeting Scheduler
  142. Missing Number In Arithmetic Progression
  143. Project Employees III
  144. Project Employees II
  145. Project Employees I
  146. Product Sales Analysis III
  147. Product Sales Analysis II
  148. Product Sales Analysis I
  149. Lexicographically Smallest Equivalent String
  150. Number of Valid Subarrays
  151. Longest Repeating Substring
  152. Missing Element in Sorted Array
  153. All Paths from Source Lead to Destination
  154. Confusing Number
  155. Minimize Rounding Error to Meet Target
  156. Campus Bikes
  157. Shortest Way to Form String
  158. Maximum Number of Ones
  159. Stepping Numbers
  160. Two Sum BSTs
  161. Intersection of Three Sorted Arrays
  162. Optimize Water Distribution in a Village
  163. Find Smallest Common Element in All Rows
  164. Minimum Knight Moves
  165. How Many Apples Can You Put into the Basket
  166. Actors and Directors Who Cooperated At Least Three Times
  167. Customers Who Bought All Products
  168. Shortest Distance to Target Color
  169. Before and After Puzzle
  170. Count Substrings with Only One Distinct Letter
  171. Minimum Cost to Connect Sticks
  172. Design File System
  173. String Transforms Into Another String
  174. Single-Row Keyboard
  175. Divide Array Into Increasing Sequences
  176. Analyze User Website Visit Pattern
  177. Minimum Swaps to Group All 1's Together
  178. Check If a Number Is Majority Element in a Sorted Array
  179. Parallel Courses
  180. Connecting Cities With Minimum Cost
  181. Path With Maximum Minimum Value
  182. Largest Unique Number
  183. Maximum Average Subtree
  184. Armstrong Number
  185. Remove Vowels from a String
  186. Number of Days in a Month
  187. The Earliest Moment When Everyone Become Friends
  188. Find K-Length Substrings With No Repeated Characters
  189. Two Sum Less Than K
  190. Sum of Digits in the Minimum Number
  191. Confusing Number II
  192. Brace Expansion
  193. Index Pairs of a String
  194. High Five
  195. Digit Count in Range
  196. Campus Bikes II
  197. Fixed Point
  198. Robot Room Cleaner
  199. Insert into a Sorted Circular Linked List
  200. Similar RGB Color
  201. Split BST
  202. Minimize Max Distance to Gas Station
  203. Search in a Sorted Array of Unknown Size
  204. Basic Calculator III
  205. Encode N-ary Tree to Binary Tree
  206. Serialize and Deserialize N-ary Tree
  207. Find Anagram Mappings
  208. Employee Free Time
  209. Bold Words in String
  210. Convert Binary Search Tree to Sorted Doubly Linked List
  211. Pour Water
  212. IP to CIDR
  213. Number Of Corner Rectangles
  214. Closest Leaf in a Binary Tree
  215. Sentence Similarity II
  216. Sentence Similarity
  217. Minimum Window Subsequence
  218. Max Stack
  219. Candy Crush
  220. Number of Distinct Islands II
  221. Number of Distinct Islands
  222. Next Closest Time
  223. K Empty Slots
  224. Path Sum IV
  225. Equal Tree Partition
  226. Remove 9
  227. Coin Path
  228. 4 Keys Keyboard
  229. Design Search Autocomplete System
  230. Maximum Average Subarray II
  231. Find the Derangement of An Array
  232. Design Log Storage System
  233. Design Excel Sum Formula
  234. Maximum Distance in Arrays
  235. Minimum Factorization
  236. Add Bold Tag in String
  237. Design Compressed String Iterator
  238. Biggest Single Number
  239. Students Report By Geography
  240. Average Salary: Departments VS Company
  241. Second Degree Follower
  242. Shortest Distance in a Line
  243. Shortest Distance in a Plane
  244. Triangle Judgement
  245. Tree Node
  246. Sales Person
  247. Consecutive Available Seats
  248. Friend Requests II: Who Has the Most Friends
  249. Design In-Memory File System
  250. Friend Requests I: Overall Acceptance Rate
  251. Kill Process
  252. Customer Placing the Largest Number of Orders
  253. Investments in 2016
  254. Find Customer Referee
  255. Count Student Number in Departments
  256. Find Cumulative Salary of an Employee
  257. Get Highest Answer Rate Question
  258. Squirrel Simulation
  259. Employee Bonus
  260. Winning Candidate
  261. Maximum Vacation Days
  262. Find Median Given Frequency of Numbers
  263. Managers with at Least 5 Direct Reports
  264. Median Employee Salary
  265. Longest Line of Consecutive One in Matrix
  266. Split Concatenated Strings
  267. Binary Tree Longest Consecutive Sequence II
  268. Split Array with Equal Sum
  269. Boundary of Binary Tree
  270. Output Contest Matches
  271. Construct Binary Tree from String
  272. Lonely Pixel II
  273. Lonely Pixel I
  274. Word Abbreviation
  275. Inorder Successor in BST II
  276. The Maze II
  277. The Maze III
  278. The Maze
  279. Max Consecutive Ones II
  280. Find Permutation
  281. Encode String with Shortest Length
  282. Convex Polygon
  283. Optimal Account Balancing
  284. Sequence Reconstruction
  285. Ternary Expression Parser
  286. Word Squares
  287. Valid Word Square
  288. Sentence Screen Fitting
  289. Minimum Unique Word Abbreviation
  290. Valid Word Abbreviation
  291. Design Phone Directory
  292. Range Addition
  293. Plus One Linked List
  294. Find Leaves of Binary Tree
  295. Nested List Weight Sum II
  296. Design Hit Counter
  297. Bomb Enemy
  298. Sort Transformed Array
  299. Logger Rate Limiter
  300. Rearrange String k Distance Apart
  301. Line Reflection
  302. Design Snake Game
  303. Android Unlock Patterns
  304. Design Tic-Tac-Toe
  305. Moving Average from Data Stream
  306. Longest Substring with At Most K Distinct Characters
  307. Nested List Weight Sum
  308. Largest BST Subtree
  309. Maximum Size Subarray Sum Equals k
  310. Number of Connected Components in an Undirected Graph
  311. Generalized Abbreviation
  312. Shortest Distance from All Buildings
  313. Binary Tree Vertical Order Traversal
  314. Sparse Matrix Multiplication
  315. Range Sum Query 2D - Mutable
  316. Number of Islands II
  317. Smallest Rectangle Enclosing Black Pixels
  318. Binary Tree Longest Consecutive Sequence
  319. Best Meeting Point
  320. Flip Game II
  321. Flip Game
  322. Word Pattern II
  323. Unique Word Abbreviation
  324. Walls and Gates
  325. Inorder Successor in BST
  326. Zigzag Iterator
  327. Wiggle Sort
  328. Find the Celebrity
  329. Paint Fence
  330. Closest Binary Search Tree Value II
  331. Encode and Decode Strings
  332. Closest Binary Search Tree Value
  333. Alien Dictionary
  334. Palindrome Permutation II
  335. Palindrome Permutation
  336. Paint House II
  337. Graph Valid Tree
  338. 3Sum Smaller
  339. Paint House
  340. Verify Preorder Sequence in Binary Search Tree
  341. Factor Combinations
  342. Meeting Rooms II
  343. Meeting Rooms
  344. Flatten 2D Vector
  345. Count Univalue Subtrees
  346. Group Shifted Strings
  347. Strobogrammatic Number III
  348. Strobogrammatic Number II
  349. Strobogrammatic Number
  350. Shortest Word Distance III
  351. Shortest Word Distance II
  352. Shortest Word Distance
  353. Reverse Words in a String II
  354. Two Sum III - Data structure design
  355. Missing Ranges
  356. One Edit Distance
  357. Longest Substring with At Most Two Distinct Characters
  358. Read N Characters Given Read4 II - Call multiple times
  359. Read N Characters Given Read4
  360. Binary Tree Upside Down