The interview plan

Ten weeks, about two hours a day. Each day is one to three lessons and three or four LeetCode problems. Every problem is free, and each lesson says what it needs. DSA runs the whole way, System Design joins in week 2, low-level design in week 7. The sixth day of every week is review: a timed drill on your weakest deck, and a mock round once there is something to mock. Networks, operating systems and databases have their own list: the fundamentals round.

Week 1 DSA first
1. Day 1Arrays and hashing
  - DSA Complexity & Big-O
  - DSA Arrays & StringsFree with an account
  - 217. Contains DuplicateEasy
  - 242. Valid AnagramEasy
  - 1. Two SumEasy
2. Day 2Arrays and hashing
  - 49. Group AnagramsMedium
  - 347. Top K Frequent ElementsMedium
  - 238. Product of Array Except SelfMedium
3. Day 3Arrays and hashing
  - 36. Valid SudokuMedium
  - 128. Longest Consecutive SequenceMedium
  - 149. Max Points on a LineHard
4. Day 4Two pointers
  - DSA Interview Patterns (recognize the shape, apply the template)With a plan
  - 125. Valid PalindromeEasy
  - 167. Two Sum II, Input Array Is SortedMedium
  - 15. 3SumMedium
5. Day 5Two pointers
  - 16. 3Sum ClosestMedium
  - 11. Container With Most WaterMedium
  - 42. Trapping Rain WaterHard
6. Day 6Review
  - A timed drill on the deck you know least
Week 2 DSA and System Design
1. Day 7Sliding window
2. Day 8Sliding window
  - System Design The order slip rail (queues & the utilization cliff)Free with an account
  - 567. Permutation in StringMedium
  - 209. Minimum Size Subarray SumMedium
  - 76. Minimum Window SubstringHard
  - 239. Sliding Window MaximumHard
3. Day 9Prefix sums
  - DSA The running total (prefix sums and difference arrays)With a plan
  - System Design The copy clerks (database replication)With a plan
  - 303. Range Sum Query, ImmutableEasy
  - 724. Find Pivot IndexEasy
  - 560. Subarray Sum Equals KMedium
  - 974. Subarray Sums Divisible by KMedium
4. Day 10Prefix sums
  - System Design Splitting the ledger (sharding)With a plan
  - 523. Continuous Subarray SumMedium
  - 304. Range Sum Query 2D, ImmutableMedium
  - 1109. Corporate Flight BookingsMedium
  - 1094. Car PoolingMedium
5. Day 11Stack and monotonic stack
  - DSA Linked Lists, Stacks & QueuesWith a plan
  - System Design The cut phone line (CAP, done properly)With a plan
  - 20. Valid ParenthesesEasy
  - 1047. Remove All Adjacent Duplicates In StringEasy
  - 155. Min StackMedium
  - 150. Evaluate Reverse Polish NotationMedium
6. Day 12Review
  - A timed drill on the deck you know least
Week 3 DSA and System Design
1. Day 13Stack and monotonic stack
  - System Design Who holds the pen (consensus & Raft)With a plan
  - 739. Daily TemperaturesMedium
  - 503. Next Greater Element IIMedium
  - 853. Car FleetMedium
  - 84. Largest Rectangle in HistogramHard
2. Day 14Binary search on an index
  - DSA Sorting & SearchingWith a plan
  - System Design The Two Ledgers Must Agree (Distributed Transactions)With a plan
  - 704. Binary SearchEasy
  - 35. Search Insert PositionEasy
  - 74. Search a 2D MatrixMedium
  - 153. Find Minimum in Rotated Sorted ArrayMedium
3. Day 15Binary search on an index
  - System Design Charged Twice (idempotency & exactly-once)With a plan
  - 33. Search in Rotated Sorted ArrayMedium
  - 981. Time Based Key-Value StoreMedium
  - 4. Median of Two Sorted ArraysHard
4. Day 16Binary search on the answer
  - DSA Clinic #33: Koko Eating BananasWith a plan
  - System Design The Ledger Everyone Reads (event-driven & the log)With a plan
  - System Design One wala, many kettles (concurrency vs parallelism)With a plan
  - 69. Sqrt(x)Easy
  - 875. Koko Eating BananasMedium
  - 1011. Capacity To Ship Packages Within D DaysMedium
  - 1482. Minimum Number of Days to Make m BouquetsMedium
  - 410. Split Array Largest SumHard
5. Day 17Linked lists and fast/slow pointers
  - DSA Clinic #34: Linked List CycleWith a plan
  - System Design The bouncer at the door (rate limiting)With a plan
  - 206. Reverse Linked ListEasy
  - 21. Merge Two Sorted ListsEasy
  - 141. Linked List CycleEasy
  - 876. Middle of the Linked ListEasy
6. Day 18Review
  - A timed drill on the deck you know least
  - A System Design mock round, 45 minutes, out loud
Week 4 DSA and System Design
1. Day 19Linked lists and fast/slow pointers
  - System Design The stall that turns people away (load shedding and admission control)With a plan
  - 143. Reorder ListMedium
  - 19. Remove Nth Node From End of ListMedium
  - 138. Copy List with Random PointerMedium
  - 2. Add Two NumbersMedium
2. Day 20Linked lists and fast/slow pointers
  - System Design Thirty stalls on one order (availability, the nines, and the tail at scale)With a plan
  - 287. Find the Duplicate NumberMedium
  - 146. LRU CacheMedium
  - 25. Reverse Nodes in k-GroupHard
3. Day 21Trees
  - DSA Trees (BST, balancing, heaps, tries)With a plan
  - System Design Why Data Is the Hard Part (the five building blocks)With a plan
  - 226. Invert Binary TreeEasy
  - 104. Maximum Depth of Binary TreeEasy
  - 543. Diameter of Binary TreeEasy
  - 100. Same TreeEasy
4. Day 22Trees
5. Day 23Trees
  - System Design The last vada (inventory contention and locking)With a plan
  - 199. Binary Tree Right Side ViewMedium
  - 1448. Count Good Nodes in Binary TreeMedium
  - 98. Validate Binary Search TreeMedium
  - 230. Kth Smallest Element in a BSTMedium
6. Day 24Review
  - A timed drill on the deck you know least
  - A System Design mock round, 45 minutes, out loud
Week 5 DSA and System Design
1. Day 25Trees
2. Day 26Tries
  - DSA Clinic #23: Implement TrieWith a plan
  - System Design The branch near your house (CDNs and object storage)With a plan
  - 14. Longest Common PrefixEasy
  - 208. Implement Trie (Prefix Tree)Medium
  - 211. Design Add and Search Words Data StructureMedium
  - 212. Word Search IIHard
3. Day 27Heaps and top-k
  - DSA Clinic #19: Kth Largest Element in an ArrayWith a plan
  - System Design Counting the crowd without a register (HyperLogLog, count-min, top-k)With a plan
  - System Design The Contract at the Counter (API design)With a plan
  - 1046. Last Stone WeightEasy
  - 703. Kth Largest Element in a StreamEasy
  - 215. Kth Largest Element in an ArrayMedium
  - 973. K Closest Points to OriginMedium
4. Day 28Heaps and top-k
  - System Design The customer who won't hang up (polling, SSE and WebSockets)With a plan
  - 621. Task SchedulerMedium
  - 355. Design TwitterMedium
  - 23. Merge k Sorted ListsHard
  - 295. Find Median from Data StreamHard
5. Day 29Backtracking
  - DSA Algorithm Design PatternsWith a plan
  - System Design A lock on every door of the stall (security inside a design)With a plan
  - 1863. Sum of All Subset XOR TotalsEasy
  - 78. SubsetsMedium
  - 39. Combination SumMedium
  - 46. PermutationsMedium
6. Day 30Review
  - A timed drill on the deck you know least
  - A System Design mock round, 45 minutes, out loud
Week 6 DSA and System Design
1. Day 31Backtracking
  - System Design Two kitchens, two cities (multi-region and active-active)With a plan
  - 90. Subsets IIMedium
  - 40. Combination Sum IIMedium
  - 79. Word SearchMedium
2. Day 32Backtracking
  - System Design What did the database promise? (consistency models)With a plan
  - 131. Palindrome PartitioningMedium
  - 17. Letter Combinations of a Phone NumberMedium
  - 51. N-QueensHard
3. Day 33Graphs: BFS, DFS and topological sort
  - DSA Graphs (BFS, DFS, Dijkstra, topological sort)With a plan
  - System Design The write that has to happen twice (CDC and the outbox)With a plan
  - 733. Flood FillEasy
  - 200. Number of IslandsMedium
  - 133. Clone GraphMedium
  - 695. Max Area of IslandMedium
4. Day 34Graphs: BFS, DFS and topological sort
  - System Design Changing the engine in flight (live schema and data migrations)With a plan
  - 417. Pacific Atlantic Water FlowMedium
  - 130. Surrounded RegionsMedium
  - 994. Rotting OrangesMedium
5. Day 35Graphs: BFS, DFS and topological sort
  - System Design One request, forty services (distributed tracing)With a plan
  - 207. Course ScheduleMedium
  - 210. Course Schedule IIMedium
  - 127. Word LadderHard
6. Day 36Review
  - A timed drill on the deck you know least
  - A System Design mock round, 45 minutes, out loud
Week 7 All three
1. Day 37Shortest paths
  - DSA Clinic #25: Network Delay TimeWith a plan
  - System Design The log is the truth (event sourcing and CQRS)With a plan
  - Low-level design Nouns and verbs (from requirements to classes)With a plan
  - 1971. Find if Path Exists in GraphEasy
  - 743. Network Delay TimeMedium
  - 1631. Path With Minimum EffortMedium
2. Day 38Shortest paths
  - System Design Design the Whole Thing (the interview, assembled)With a plan
  - System Design Four Systems in One Night (worked designs)With a plan
  - Low-level design The object that keeps its own rules (encapsulation and invariants)With a plan
  - 787. Cheapest Flights Within K StopsMedium
  - 1584. Min Cost to Connect All PointsMedium
  - 778. Swim in Rising WaterHard
3. Day 39Union-find
  - DSA Clinic #26: Redundant ConnectionWith a plan
  - System Design The stall, built: one counter in code (load balancing, health checks and caching in Go)With a plan
  - Low-level design Has-a beats is-a (composition over inheritance)With a plan
  - 547. Number of ProvincesMedium
  - 684. Redundant ConnectionMedium
  - 990. Satisfiability of Equality EquationsMedium
  - 721. Accounts MergeMedium
  - 1579. Remove Max Number of Edges to Keep Graph Fully TraversableHard
4. Day 40Intervals
  - DSA Clinic #28: Merge IntervalsWith a plan
  - System Design The stall, built: copies and shards (replication and sharding in Go)With a plan
  - Low-level design Five letters, one shop (SOLID)With a plan
  - 228. Summary RangesEasy
  - 56. Merge IntervalsMedium
  - 57. Insert IntervalMedium
  - 435. Non-overlapping IntervalsMedium
5. Day 41Intervals
6. Day 42Review
  - A timed drill on the deck you know least
  - A System Design mock round, 45 minutes, out loud
Week 8 All three
1. Day 43Greedy
  - DSA Clinic #27: Jump GameWith a plan
  - System Design Design a web crawler (a billion pages a month, politely)With a plan
  - Low-level design Swap the rule, keep the class (Strategy and Factory)With a plan
  - 455. Assign CookiesEasy
  - 53. Maximum SubarrayMedium
  - 55. Jump GameMedium
2. Day 44Greedy
  - System Design Counting clicks in real time (ad click aggregation and top-k)With a plan
  - Low-level design Tell everyone who cares (Observer and State)With a plan
  - 45. Jump Game IIMedium
  - 134. Gas StationMedium
  - 846. Hand of StraightsMedium
3. Day 45Greedy
  - System Design The ten o'clock rush (ticket booking under a flash sale)With a plan
  - Low-level design Design a parking lot (the first whole round)With a plan
  - 763. Partition LabelsMedium
  - 678. Valid Parenthesis StringMedium
  - 1326. Minimum Number of Taps to Open to Water a GardenHard
4. Day 461-D dynamic programming
  - DSA Recursion & Dynamic ProgrammingWith a plan
  - System Design Run this at nine (a distributed job scheduler)With a plan
  - Low-level design Design an elevator (a state machine with a scheduler)With a plan
  - 70. Climbing StairsEasy
  - 746. Min Cost Climbing StairsEasy
  - 198. House RobberMedium
5. Day 471-D dynamic programming
  - System Design Is it up? (metrics and monitoring)With a plan
  - 213. House Robber IIMedium
  - 5. Longest Palindromic SubstringMedium
  - 91. Decode WaysMedium
6. Day 48Review
  - A timed drill on the deck you know least
  - A low-level design mock round, 45 minutes, out loud
Week 9 All three
1. Day 491-D dynamic programming
  - Low-level design Two people, one seat (thread-safe booking)With a plan
  - 322. Coin ChangeMedium
  - 152. Maximum Product SubarrayMedium
  - 139. Word BreakMedium
2. Day 501-D dynamic programming
  - Low-level design Who owes whom (design Splitwise)With a plan
  - 300. Longest Increasing SubsequenceMedium
  - 518. Coin Change IIMedium
  - 32. Longest Valid ParenthesesHard
3. Day 512-D dynamic programming
  - DSA Dynamic Programming, Worked (filling the table)With a plan
  - Low-level design Design an LRU cache (a map and a list that keep each other honest)With a plan
  - 118. Pascal's TriangleEasy
  - 62. Unique PathsMedium
  - 1143. Longest Common SubsequenceMedium
  - 309. Best Time to Buy and Sell Stock with CooldownMedium
4. Day 522-D dynamic programming
  - Low-level design Design a vending machine (states that refuse)With a plan
  - 494. Target SumMedium
  - 72. Edit DistanceMedium
  - 97. Interleaving StringMedium
5. Day 532-D dynamic programming
6. Day 54Review
  - A timed drill on the deck you know least
  - A System Design mock round, 45 minutes, out loud
Week 10 All three
1. Day 55Bits and math
  - DSA Bit Manipulation (thinking in bits)With a plan
  - Low-level design Design a rate limiter (the class inside the bouncer)With a plan
  - 136. Single NumberEasy
  - 191. Number of 1 BitsEasy
  - 338. Counting BitsEasy
2. Day 56Bits and math
  - Low-level design Design a logger (levels, handlers and the one instance)With a plan
  - 268. Missing NumberEasy
  - 190. Reverse BitsEasy
3. Day 57Bits and math
  - Low-level design Design chess (pieces that know their own moves)With a plan
  - 371. Sum of Two IntegersMedium
  - 48. Rotate ImageMedium
4. Day 58Bits and math
  - Low-level design Design snake and ladder (a game you can test)With a plan
  - 54. Spiral MatrixMedium
  - 50. Pow(x, n)Medium
5. Day 59Bits and math
  - 260. Single Number IIIMedium
  - 1835. Find XOR Sum of All Pairs Bitwise ANDHard
6. Day 60Review
  - A timed drill on the deck you know least
  - A low-level design mock round, 45 minutes, out loud

Every problem is a free LeetCode problem, checked against LeetCode's own index. The whole set, pattern by pattern, is on the problem sets. Ticks follow you to any device you sign in on. A lesson ticks itself when you mark it read, or tick it here if you skip it.

The interview plan

Week 1 DSA first

Day 1Arrays and hashing

Day 2Arrays and hashing

Day 3Arrays and hashing

Day 4Two pointers

Day 5Two pointers

Day 6Review

Week 2 DSA and System Design

Day 7Sliding window

Day 8Sliding window

Day 9Prefix sums

Day 10Prefix sums

Day 11Stack and monotonic stack

Day 12Review

Week 3 DSA and System Design

Day 13Stack and monotonic stack

Day 14Binary search on an index

Day 15Binary search on an index

Day 16Binary search on the answer

Day 17Linked lists and fast/slow pointers

Day 18Review

Week 4 DSA and System Design

Day 19Linked lists and fast/slow pointers

Day 20Linked lists and fast/slow pointers

Day 21Trees

Day 22Trees

Day 23Trees

Day 24Review

Week 5 DSA and System Design

Day 25Trees

Day 26Tries

Day 27Heaps and top-k

Day 28Heaps and top-k

Day 29Backtracking

Day 30Review

Week 6 DSA and System Design

Day 31Backtracking

Day 32Backtracking

Day 33Graphs: BFS, DFS and topological sort

Day 34Graphs: BFS, DFS and topological sort

Day 35Graphs: BFS, DFS and topological sort

Day 36Review

Week 7 All three

Day 37Shortest paths

Day 38Shortest paths

Day 39Union-find

Day 40Intervals

Day 41Intervals

Day 42Review

Week 8 All three

Day 43Greedy

Day 44Greedy

Day 45Greedy

Day 461-D dynamic programming

Day 471-D dynamic programming

Day 48Review

Week 9 All three

Day 491-D dynamic programming

Day 501-D dynamic programming

Day 512-D dynamic programming

Day 522-D dynamic programming

Day 532-D dynamic programming

Day 54Review

Week 10 All three

Day 55Bits and math

Day 56Bits and math

Day 57Bits and math

Day 58Bits and math

Day 59Bits and math

Day 60Review