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Our most popular plan previously sold for $299 and is now only $13/month. This plan saves you over 60% in comparison to the monthly plan. (prices are marked in USD)

 Lightning Judge

Tired of waiting? Premium users get priority judging using an exclusive queue, resulting in a 3X shorter wait time, up to 10X during peak hours.

∞  Unlimited Playgrounds

Premium users can create an unlimited number of Playgrounds, up from 10! You also get the ability to organize your Playgrounds in folders.

 Interview Simulations

Mock interviews provide you with a way to test your abilities in a timed setting, just like a coding challenge or on-site interview. You choose the company and we will select an appropriate question from our constantly growing database.

 Sort Questions by Prevalence

Find out which questions turn up most frequently in interviews so that you know where to focus your personal studying. Invaluable data collected from thousands of samples.

 Access to Premium Content

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.

 Select Questions by Company

Target your studying more accurately towards your dream job. Find out which companies asked which questions, we have nearly 200 questions from Google alone.

~ 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?

You will continue to have access to it all, it isn't going anywhere.

I clicked the subscribe button, fill in the credit card information and clicked "Add Payment Method". I still can't access the exclusive problems.

You may access My Subscription page to confirm your subscription. Please check your billing history to make sure the transaction went through. If it shows no new transaction, it means your card was probably declined. Please try subscribe again using another debit/credit card or contact your bank to inquire for more information. If you still encounter problems, contact us.

What if I sign up and want to cancel?

You can cancel your subscription at any time here. After cancellation your subscription will remain active until the current time period is finished.

What are the premium questions?   Show

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

  1. Average Selling Price
  2. Web Crawler Multithreaded
  3. Number of Comments per Post
  4. Web Crawler
  5. Report Contiguous Dates
  6. Team Scores in Football Tournament
  7. Queries Quality and Percentage
  8. Monthly Transactions II
  9. Last Person to Fit in the Elevator
  10. Tournament Winners
  11. Monthly Transactions I
  12. Design Bounded Blocking Queue
  13. Immediate Food Delivery II
  14. Immediate Food Delivery I
  15. Diet Plan Performance
  16. Product Price at a Given Date
  17. Market Analysis II
  18. Market Analysis I
  19. Article Views II
  20. Article Views I
  21. User Activity for the Past 30 Days II
  22. User Activity for the Past 30 Days I
  23. Reported Posts II
  24. User Purchase Platform
  25. Active Businesses
  26. Reported Posts
  27. Highest Grade For Each Student
  28. New Users Daily Count
  29. Palindrome Removal
  30. Unpopular Books
  31. Game Play Analysis V
  32. Divide Chocolate
  33. Game Play Analysis IV
  34. Game Play Analysis III
  35. Game Play Analysis II
  36. Game Play Analysis I
  37. Valid Palindrome III
  38. Tree Diameter
  39. Design A Leaderboard
  40. Array Transformation
  41. Sales Analysis III
  42. Sales Analysis II
  43. Sales Analysis I
  44. Minimum Time to Build Blocks
  45. Toss Strange Coins
  46. Meeting Scheduler
  47. Missing Number In Arithmetic Progression
  48. Project Employees III
  49. Project Employees II
  50. Project Employees I
  51. Product Sales Analysis III
  52. Product Sales Analysis II
  53. Product Sales Analysis I
  54. Lexicographically Smallest Equivalent String
  55. Number of Valid Subarrays
  56. Longest Repeating Substring
  57. Missing Element in Sorted Array
  58. All Paths from Source Lead to Destination
  59. Confusing Number
  60. Minimize Rounding Error to Meet Target
  61. Campus Bikes
  62. Shortest Way to Form String
  63. Maximum Number of Ones
  64. Stepping Numbers
  65. Two Sum BSTs
  66. Intersection of Three Sorted Arrays
  67. Optimize Water Distribution in a Village
  68. Find Smallest Common Element in All Rows
  69. Minimum Knight Moves
  70. How Many Apples Can You Put into the Basket
  71. Actors and Directors Who Cooperated At Least Three Times
  72. Customers Who Bought All Products
  73. Shortest Distance to Target Color
  74. Before and After Puzzle
  75. Count Substrings with Only One Distinct Letter
  76. Minimum Cost to Connect Sticks
  77. Design File System
  78. String Transforms Into Another String
  79. Single-Row Keyboard
  80. Divide Array Into Increasing Sequences
  81. Analyze User Website Visit Pattern
  82. Minimum Swaps to Group All 1's Together
  83. Check If a Number Is Majority Element in a Sorted Array
  84. Parallel Courses
  85. Connecting Cities With Minimum Cost
  86. Path With Maximum Minimum Value
  87. Largest Unique Number
  88. Maximum Average Subtree
  89. Armstrong Number
  90. Remove Vowels from a String
  91. Number of Days in a Month
  92. The Earliest Moment When Everyone Become Friends
  93. Find K-Length Substrings With No Repeated Characters
  94. Two Sum Less Than K
  95. Sum of Digits in the Minimum Number
  96. Confusing Number II
  97. Brace Expansion
  98. Index Pairs of a String
  99. High Five
  100. Digit Count in Range
  101. Campus Bikes II
  102. Fixed Point
  103. Robot Room Cleaner
  104. Insert into a Cyclic Sorted List
  105. Similar RGB Color
  106. Split BST
  107. Minimize Max Distance to Gas Station
  108. Search in a Sorted Array of Unknown Size
  109. Basic Calculator III
  110. Encode N-ary Tree to Binary Tree
  111. Serialize and Deserialize N-ary Tree
  112. Find Anagram Mappings
  113. Employee Free Time
  114. Bold Words in String
  115. Convert Binary Search Tree to Sorted Doubly Linked List
  116. Pour Water
  117. IP to CIDR
  118. Number Of Corner Rectangles
  119. Closest Leaf in a Binary Tree
  120. Sentence Similarity II
  121. Sentence Similarity
  122. Minimum Window Subsequence
  123. Max Stack
  124. Candy Crush
  125. Number of Distinct Islands II
  126. Number of Distinct Islands
  127. Next Closest Time
  128. K Empty Slots
  129. Path Sum IV
  130. Equal Tree Partition
  131. Remove 9
  132. Coin Path
  133. 4 Keys Keyboard
  134. Design Search Autocomplete System
  135. Maximum Average Subarray II
  136. Find the Derangement of An Array
  137. Design Log Storage System
  138. Design Excel Sum Formula
  139. Maximum Distance in Arrays
  140. Minimum Factorization
  141. Add Bold Tag in String
  142. Design Compressed String Iterator
  143. Biggest Single Number
  144. Students Report By Geography
  145. Average Salary: Departments VS Company
  146. Second Degree Follower
  147. Shortest Distance in a Line
  148. Shortest Distance in a Plane
  149. Triangle Judgement
  150. Tree Node
  151. Sales Person
  152. Consecutive Available Seats
  153. Friend Requests II: Who Has the Most Friends
  154. Design In-Memory File System
  155. Friend Requests I: Overall Acceptance Rate
  156. Kill Process
  157. Customer Placing the Largest Number of Orders
  158. Investments in 2016
  159. Find Customer Referee
  160. Count Student Number in Departments
  161. Find Cumulative Salary of an Employee
  162. Get Highest Answer Rate Question
  163. Squirrel Simulation
  164. Employee Bonus
  165. Winning Candidate
  166. Maximum Vacation Days
  167. Find Median Given Frequency of Numbers
  168. Managers with at Least 5 Direct Reports
  169. Median Employee Salary
  170. Longest Line of Consecutive One in Matrix
  171. Split Concatenated Strings
  172. Binary Tree Longest Consecutive Sequence II
  173. Split Array with Equal Sum
  174. Boundary of Binary Tree
  175. Output Contest Matches
  176. Construct Binary Tree from String
  177. Lonely Pixel II
  178. Lonely Pixel I
  179. Word Abbreviation
  180. Inorder Successor in BST II
  181. The Maze II
  182. The Maze III
  183. The Maze
  184. Max Consecutive Ones II
  185. Find Permutation
  186. Encode String with Shortest Length
  187. Convex Polygon
  188. Optimal Account Balancing
  189. Sequence Reconstruction
  190. Ternary Expression Parser
  191. Word Squares
  192. Valid Word Square
  193. Sentence Screen Fitting
  194. Minimum Unique Word Abbreviation
  195. Valid Word Abbreviation
  196. Design Phone Directory
  197. Range Addition
  198. Plus One Linked List
  199. Find Leaves of Binary Tree
  200. Nested List Weight Sum II
  201. Design Hit Counter
  202. Bomb Enemy
  203. Sort Transformed Array
  204. Logger Rate Limiter
  205. Rearrange String k Distance Apart
  206. Line Reflection
  207. Design Snake Game
  208. Android Unlock Patterns
  209. Design Tic-Tac-Toe
  210. Moving Average from Data Stream
  211. Longest Substring with At Most K Distinct Characters
  212. Nested List Weight Sum
  213. Largest BST Subtree
  214. Maximum Size Subarray Sum Equals k
  215. Number of Connected Components in an Undirected Graph
  216. Generalized Abbreviation
  217. Shortest Distance from All Buildings
  218. Binary Tree Vertical Order Traversal
  219. Sparse Matrix Multiplication
  220. Range Sum Query 2D - Mutable
  221. Number of Islands II
  222. Smallest Rectangle Enclosing Black Pixels
  223. Binary Tree Longest Consecutive Sequence
  224. Best Meeting Point
  225. Flip Game II
  226. Flip Game
  227. Word Pattern II
  228. Unique Word Abbreviation
  229. Walls and Gates
  230. Inorder Successor in BST
  231. Zigzag Iterator
  232. Wiggle Sort
  233. Find the Celebrity
  234. Paint Fence
  235. Closest Binary Search Tree Value II
  236. Encode and Decode Strings
  237. Closest Binary Search Tree Value
  238. Alien Dictionary
  239. Palindrome Permutation II
  240. Palindrome Permutation
  241. Paint House II
  242. Graph Valid Tree
  243. 3Sum Smaller
  244. Paint House
  245. Verify Preorder Sequence in Binary Search Tree
  246. Factor Combinations
  247. Meeting Rooms II
  248. Meeting Rooms
  249. Flatten 2D Vector
  250. Count Univalue Subtrees
  251. Group Shifted Strings
  252. Strobogrammatic Number III
  253. Strobogrammatic Number II
  254. Strobogrammatic Number
  255. Shortest Word Distance III
  256. Shortest Word Distance II
  257. Shortest Word Distance
  258. Reverse Words in a String II
  259. Two Sum III - Data structure design
  260. Missing Ranges
  261. One Edit Distance
  262. Longest Substring with At Most Two Distinct Characters
  263. Read N Characters Given Read4 II - Call multiple times
  264. Read N Characters Given Read4
  265. Binary Tree Upside Down