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 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. Find the Start and End Number of Continuous Ranges
  2. Students and Examinations
  3. Traffic Light Controlled Intersection
  4. All People Report to the Given Manager
  5. Print Immutable Linked List in Reverse
  6. Page Recommendations
  7. Average Selling Price
  8. Web Crawler Multithreaded
  9. Number of Comments per Post
  10. Web Crawler
  11. Report Contiguous Dates
  12. Team Scores in Football Tournament
  13. Queries Quality and Percentage
  14. Monthly Transactions II
  15. Last Person to Fit in the Elevator
  16. Tournament Winners
  17. Monthly Transactions I
  18. Design Bounded Blocking Queue
  19. Immediate Food Delivery II
  20. Immediate Food Delivery I
  21. Diet Plan Performance
  22. Product Price at a Given Date
  23. Market Analysis II
  24. Market Analysis I
  25. Article Views II
  26. Article Views I
  27. User Activity for the Past 30 Days II
  28. User Activity for the Past 30 Days I
  29. Reported Posts II
  30. Number of Ships in a Rectangle
  31. User Purchase Platform
  32. Active Businesses
  33. Reported Posts
  34. Highest Grade For Each Student
  35. Handshakes That Don't Cross
  36. New Users Daily Count
  37. Palindrome Removal
  38. Delete Tree Nodes
  39. Remove Interval
  40. Hexspeak
  41. Unpopular Books
  42. Game Play Analysis V
  43. Divide Chocolate
  44. Synonymous Sentences
  45. Smallest Common Region
  46. Encode Number
  47. Game Play Analysis IV
  48. Game Play Analysis III
  49. Game Play Analysis II
  50. Game Play Analysis I
  51. Valid Palindrome III
  52. Tree Diameter
  53. Design A Leaderboard
  54. Array Transformation
  55. Sales Analysis III
  56. Sales Analysis II
  57. Sales Analysis I
  58. Minimum Time to Build Blocks
  59. Toss Strange Coins
  60. Meeting Scheduler
  61. Missing Number In Arithmetic Progression
  62. Project Employees III
  63. Project Employees II
  64. Project Employees I
  65. Product Sales Analysis III
  66. Product Sales Analysis II
  67. Product Sales Analysis I
  68. Lexicographically Smallest Equivalent String
  69. Number of Valid Subarrays
  70. Longest Repeating Substring
  71. Missing Element in Sorted Array
  72. All Paths from Source Lead to Destination
  73. Confusing Number
  74. Minimize Rounding Error to Meet Target
  75. Campus Bikes
  76. Shortest Way to Form String
  77. Maximum Number of Ones
  78. Stepping Numbers
  79. Two Sum BSTs
  80. Intersection of Three Sorted Arrays
  81. Optimize Water Distribution in a Village
  82. Find Smallest Common Element in All Rows
  83. Minimum Knight Moves
  84. How Many Apples Can You Put into the Basket
  85. Actors and Directors Who Cooperated At Least Three Times
  86. Customers Who Bought All Products
  87. Shortest Distance to Target Color
  88. Before and After Puzzle
  89. Count Substrings with Only One Distinct Letter
  90. Minimum Cost to Connect Sticks
  91. Design File System
  92. String Transforms Into Another String
  93. Single-Row Keyboard
  94. Divide Array Into Increasing Sequences
  95. Analyze User Website Visit Pattern
  96. Minimum Swaps to Group All 1's Together
  97. Check If a Number Is Majority Element in a Sorted Array
  98. Parallel Courses
  99. Connecting Cities With Minimum Cost
  100. Path With Maximum Minimum Value
  101. Largest Unique Number
  102. Maximum Average Subtree
  103. Armstrong Number
  104. Remove Vowels from a String
  105. Number of Days in a Month
  106. The Earliest Moment When Everyone Become Friends
  107. Find K-Length Substrings With No Repeated Characters
  108. Two Sum Less Than K
  109. Sum of Digits in the Minimum Number
  110. Confusing Number II
  111. Brace Expansion
  112. Index Pairs of a String
  113. High Five
  114. Digit Count in Range
  115. Campus Bikes II
  116. Fixed Point
  117. Robot Room Cleaner
  118. Insert into a Sorted Circular Linked List
  119. Similar RGB Color
  120. Split BST
  121. Minimize Max Distance to Gas Station
  122. Search in a Sorted Array of Unknown Size
  123. Basic Calculator III
  124. Encode N-ary Tree to Binary Tree
  125. Serialize and Deserialize N-ary Tree
  126. Find Anagram Mappings
  127. Employee Free Time
  128. Bold Words in String
  129. Convert Binary Search Tree to Sorted Doubly Linked List
  130. Pour Water
  131. IP to CIDR
  132. Number Of Corner Rectangles
  133. Closest Leaf in a Binary Tree
  134. Sentence Similarity II
  135. Sentence Similarity
  136. Minimum Window Subsequence
  137. Max Stack
  138. Candy Crush
  139. Number of Distinct Islands II
  140. Number of Distinct Islands
  141. Next Closest Time
  142. K Empty Slots
  143. Path Sum IV
  144. Equal Tree Partition
  145. Remove 9
  146. Coin Path
  147. 4 Keys Keyboard
  148. Design Search Autocomplete System
  149. Maximum Average Subarray II
  150. Find the Derangement of An Array
  151. Design Log Storage System
  152. Design Excel Sum Formula
  153. Maximum Distance in Arrays
  154. Minimum Factorization
  155. Add Bold Tag in String
  156. Design Compressed String Iterator
  157. Biggest Single Number
  158. Students Report By Geography
  159. Average Salary: Departments VS Company
  160. Second Degree Follower
  161. Shortest Distance in a Line
  162. Shortest Distance in a Plane
  163. Triangle Judgement
  164. Tree Node
  165. Sales Person
  166. Consecutive Available Seats
  167. Friend Requests II: Who Has the Most Friends
  168. Design In-Memory File System
  169. Friend Requests I: Overall Acceptance Rate
  170. Kill Process
  171. Customer Placing the Largest Number of Orders
  172. Investments in 2016
  173. Find Customer Referee
  174. Count Student Number in Departments
  175. Find Cumulative Salary of an Employee
  176. Get Highest Answer Rate Question
  177. Squirrel Simulation
  178. Employee Bonus
  179. Winning Candidate
  180. Maximum Vacation Days
  181. Find Median Given Frequency of Numbers
  182. Managers with at Least 5 Direct Reports
  183. Median Employee Salary
  184. Longest Line of Consecutive One in Matrix
  185. Split Concatenated Strings
  186. Binary Tree Longest Consecutive Sequence II
  187. Split Array with Equal Sum
  188. Boundary of Binary Tree
  189. Output Contest Matches
  190. Construct Binary Tree from String
  191. Lonely Pixel II
  192. Lonely Pixel I
  193. Word Abbreviation
  194. Inorder Successor in BST II
  195. The Maze II
  196. The Maze III
  197. The Maze
  198. Max Consecutive Ones II
  199. Find Permutation
  200. Encode String with Shortest Length
  201. Convex Polygon
  202. Optimal Account Balancing
  203. Sequence Reconstruction
  204. Ternary Expression Parser
  205. Word Squares
  206. Valid Word Square
  207. Sentence Screen Fitting
  208. Minimum Unique Word Abbreviation
  209. Valid Word Abbreviation
  210. Design Phone Directory
  211. Range Addition
  212. Plus One Linked List
  213. Find Leaves of Binary Tree
  214. Nested List Weight Sum II
  215. Design Hit Counter
  216. Bomb Enemy
  217. Sort Transformed Array
  218. Logger Rate Limiter
  219. Rearrange String k Distance Apart
  220. Line Reflection
  221. Design Snake Game
  222. Android Unlock Patterns
  223. Design Tic-Tac-Toe
  224. Moving Average from Data Stream
  225. Longest Substring with At Most K Distinct Characters
  226. Nested List Weight Sum
  227. Largest BST Subtree
  228. Maximum Size Subarray Sum Equals k
  229. Number of Connected Components in an Undirected Graph
  230. Generalized Abbreviation
  231. Shortest Distance from All Buildings
  232. Binary Tree Vertical Order Traversal
  233. Sparse Matrix Multiplication
  234. Range Sum Query 2D - Mutable
  235. Number of Islands II
  236. Smallest Rectangle Enclosing Black Pixels
  237. Binary Tree Longest Consecutive Sequence
  238. Best Meeting Point
  239. Flip Game II
  240. Flip Game
  241. Word Pattern II
  242. Unique Word Abbreviation
  243. Walls and Gates
  244. Inorder Successor in BST
  245. Zigzag Iterator
  246. Wiggle Sort
  247. Find the Celebrity
  248. Paint Fence
  249. Closest Binary Search Tree Value II
  250. Encode and Decode Strings
  251. Closest Binary Search Tree Value
  252. Alien Dictionary
  253. Palindrome Permutation II
  254. Palindrome Permutation
  255. Paint House II
  256. Graph Valid Tree
  257. 3Sum Smaller
  258. Paint House
  259. Verify Preorder Sequence in Binary Search Tree
  260. Factor Combinations
  261. Meeting Rooms II
  262. Meeting Rooms
  263. Flatten 2D Vector
  264. Count Univalue Subtrees
  265. Group Shifted Strings
  266. Strobogrammatic Number III
  267. Strobogrammatic Number II
  268. Strobogrammatic Number
  269. Shortest Word Distance III
  270. Shortest Word Distance II
  271. Shortest Word Distance
  272. Reverse Words in a String II
  273. Two Sum III - Data structure design
  274. Missing Ranges
  275. One Edit Distance
  276. Longest Substring with At Most Two Distinct Characters
  277. Read N Characters Given Read4 II - Call multiple times
  278. Read N Characters Given Read4
  279. Binary Tree Upside Down