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Course · Interview foundations

DSA

DSA rounds in Data Engineering interviews are usually easy to medium problems on arrays, hashing, strings, two pointers and sliding windows, sometimes graphs or DP.

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Lessons
16
Interview questions
249
Projects & case studies
0
Reading time
~5 h

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Course structure

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Practice

249 problems in 17 topics, from basic to advanced. 0 of 249 done.

Arrays0/20

Pattern lesson: Arrays and Hashing: Sets, Hash Maps, Prefix Sums and Intervals

Array Basics1

  1. Majority ElementEasyLeetCode

Prefix Sum6

  1. Find Pivot IndexEasyLeetCode
  2. Product of Array Except SelfMediumLeetCode
  3. Subarray Sum Equals KMediumLeetCode
  4. Subarray Sums Divisible by KMediumLeetCode
  5. Contiguous ArrayMediumLeetCode
  6. Shortest Subarray with Sum at Least KHardLeetCode

Kadane's Algorithm5

  1. Maximum SubarrayMediumLeetCode
  2. Maximum Product SubarrayMediumLeetCode
  3. Maximum Subarray Sum with One DeletionMediumLeetCode
  4. Maximum Absolute Sum of Any SubarrayMediumLeetCode
  5. Maximum Sum Circular SubarrayMediumLeetCode

Matrix3

  1. Rotate ImageMediumLeetCode
  2. Spiral MatrixMediumLeetCode
  3. Set Matrix ZeroesMediumLeetCode

Cyclic Sort5

  1. Missing NumberEasyLeetCode
  2. Find All Numbers Disappeared in an ArrayEasyLeetCode
  3. Set MismatchEasyLeetCode
  4. Find All Duplicates in an ArrayMediumLeetCode
  5. First Missing PositiveHardLeetCode
Hashing0/9

Pattern lesson: Arrays and Hashing: Sets, Hash Maps, Prefix Sums and Intervals

  1. Contains DuplicateEasyLeetCode
  2. Valid AnagramEasyLeetCode
  3. Two SumEasyLeetCode
  4. First Unique Character in a StringEasyLeetCode
  5. Longest PalindromeEasyLeetCode
  6. Ransom NoteEasyLeetCode
  7. Valid SudokuMediumLeetCode
  8. Group AnagramsMediumLeetCode
  9. Longest Consecutive SequenceMediumLeetCode
Strings0/4

Pattern lesson: Strings for Coding Interviews: Immutability, Scanning and Parsing

  1. Longest Common PrefixEasyLeetCode
  2. Reverse StringEasyLeetCode
  3. Encode and Decode StringsMediumGeeksforGeeks
  4. String to Integer (atoi)MediumLeetCode
Bit Manipulation0/7

Pattern lesson: Arrays and Hashing: Sets, Hash Maps, Prefix Sums and Intervals

  1. Number of 1 BitsEasyLeetCode
  2. Reverse BitsEasyLeetCode
  3. Single NumberEasyLeetCode
  4. Counting BitsEasyLeetCode
  5. Complement of Base 10 IntegerEasyLeetCode
  6. Sum of Two IntegersMediumLeetCode
  7. Single Number IIIMediumLeetCode
Two Pointers0/17

Pattern lesson: Two Pointers: Converging, Read-Write and Partitioning Templates

  1. Valid Palindrome IIEasyLeetCode
  2. Valid PalindromeEasyLeetCode
  3. Move ZeroesEasyLeetCode
  4. Remove Duplicates from Sorted ArrayEasyLeetCode
  5. Squares of a Sorted ArrayEasyLeetCode
  6. Segregate 0s and 1sEasyGeeksforGeeks
  7. Backspace String CompareEasyLeetCode
  8. Two Sum IIMediumLeetCode
  9. 3SumMediumLeetCode
  10. Container With Most WaterMediumLeetCode
  11. Sort ColorsMediumLeetCode
  12. 3Sum ClosestMediumLeetCode
  13. Triplets with Smaller SumMediumGeeksforGeeks
  14. Subarray Product Less Than KMediumLeetCode
  15. 4SumMediumLeetCode
  16. Shortest Unsorted Continuous SubarrayMediumLeetCode
  17. Trapping Rain WaterHardLeetCode
Queue0/4

Pattern lesson: Queues: FIFO Buffers, Ring Buffers and Queue Design Problems

  1. Implement Stack using QueuesEasyLeetCode
  2. Implement Queue using StacksEasyLeetCode
  3. Number of Recent CallsEasyLeetCode
  4. Design Circular QueueMediumLeetCode
Sliding Window0/14

Pattern lesson: Sliding Window: Fixed, Variable and Monotonic-Deque Templates

  1. Best Time to Buy and Sell StockEasyLeetCode
  2. Maximum Average Subarray IEasyLeetCode
  3. Max Sum Subarray of Size KEasyGeeksforGeeks
  4. Longest Substring Without Repeating CharactersMediumLeetCode
  5. Longest Repeating Character ReplacementMediumLeetCode
  6. Permutation in StringMediumLeetCode
  7. Minimum Size Subarray SumMediumLeetCode
  8. Longest K Unique Characters SubstringMediumGeeksforGeeks
  9. Fruit Into BasketsMediumLeetCode
  10. Max Consecutive Ones IIIMediumLeetCode
  11. Find All Anagrams in a StringMediumLeetCode
  12. Minimum Window SubstringHardLeetCode
  13. Sliding Window MaximumHardLeetCode
  14. Substring with Concatenation of All WordsHardLeetCode
Stack0/14

Pattern lesson: Stacks: Matching, Evaluation and Monotonic Stack Templates

Stack Basics6

  1. Valid ParenthesesEasyLeetCode
  2. Remove All Adjacent Duplicates In StringEasyLeetCode
  3. Min StackMediumLeetCode
  4. Evaluate Reverse Polish NotationMediumLeetCode
  5. Remove All Adjacent Duplicates in String IIMediumLeetCode
  6. Simplify PathMediumLeetCode

Monotonic Stack8

  1. Next Greater Element IEasyLeetCode
  2. Daily TemperaturesMediumLeetCode
  3. Car FleetMediumLeetCode
  4. Next Greater Element IIMediumLeetCode
  5. Remove Nodes From Linked ListMediumLeetCode
  6. Remove K DigitsMediumLeetCode
  7. 132 PatternMediumLeetCode
  8. Largest Rectangle in HistogramHardLeetCode
Binary Search0/20

Pattern lesson: Binary Search: Exact Match, Boundaries and Searching the Answer

Classic Binary Search6

  1. Binary SearchEasyLeetCode
  2. Ceil in Sorted ArrayEasyGeeksforGeeks
  3. Time Based Key-Value StoreMediumLeetCode
  4. Find First and Last Position of a ValueMediumLeetCode
  5. Number of OccurrenceMediumGeeksforGeeks
  6. Median of Two Sorted ArraysHardLeetCode

Rotated Arrays and Peaks5

  1. Find Rotation CountEasyGeeksforGeeks
  2. Find Minimum in Rotated Sorted ArrayMediumLeetCode
  3. Search in Rotated Sorted ArrayMediumLeetCode
  4. Peak Index in a Mountain ArrayMediumLeetCode
  5. Find Peak ElementMediumLeetCode

Binary Search on the Answer6

  1. Koko Eating BananasMediumLeetCode
  2. Minimum Number of Days to Make m BouquetsMediumLeetCode
  3. Aggressive CowsMediumGeeksforGeeks
  4. Maximum Candies Allocated to K ChildrenMediumLeetCode
  5. Capacity To Ship Packages Within D DaysMediumLeetCode
  6. Split Array Largest SumHardLeetCode

Matrix Search3

  1. Search a 2D MatrixMediumLeetCode
  2. Search a 2D Matrix IIMediumLeetCode
  3. Kth Smallest Element in a Sorted MatrixMediumLeetCode
Linked List0/18

Pattern lesson: Linked Lists: Pointer Rewiring, Fast and Slow Pointers, LRU Cache

Linked List Basics5

  1. Merge Two Sorted ListsEasyLeetCode
  2. Remove Nth Node From End of ListMediumLeetCode
  3. Copy List with Random PointerMediumLeetCode
  4. Add Two NumbersMediumLeetCode
  5. LRU CacheMediumLeetCode

Fast and Slow Pointers8

  1. Linked List CycleEasyLeetCode
  2. Happy NumberEasyLeetCode
  3. Middle of the Linked ListEasyLeetCode
  4. Palindrome Linked ListEasyLeetCode
  5. Reorder ListMediumLeetCode
  6. Find the Duplicate NumberMediumLeetCode
  7. Linked List Cycle IIMediumLeetCode
  8. Circular Array LoopMediumLeetCode

In-place Reversal5

  1. Reverse Linked ListEasyLeetCode
  2. Reverse Linked List IIMediumLeetCode
  3. Swap Nodes in PairsMediumLeetCode
  4. Rotate ListMediumLeetCode
  5. Reverse Nodes in k-GroupHardLeetCode
Trees0/18

Pattern lesson: Binary Trees and Tries: DFS, BFS and Prefix Search Templates

Tree DFS11

  1. Invert Binary TreeEasyLeetCode
  2. Maximum Depth of Binary TreeEasyLeetCode
  3. Diameter of Binary TreeEasyLeetCode
  4. Balanced Binary TreeEasyLeetCode
  5. Same TreeEasyLeetCode
  6. Subtree of Another TreeEasyLeetCode
  7. Count Good Nodes in Binary TreeMediumLeetCode
  8. Construct Binary Tree from Preorder and Inorder TraversalMediumLeetCode
  9. Lowest Common Ancestor of a Binary TreeMediumLeetCode
  10. Binary Tree Maximum Path SumHardLeetCode
  11. Serialize and Deserialize Binary TreeHardLeetCode

Tree BFS2

  1. Binary Tree Level Order TraversalMediumLeetCode
  2. Binary Tree Right Side ViewMediumLeetCode

Trie5

  1. Implement Trie (Prefix Tree)MediumLeetCode
  2. Design Add and Search WordsMediumLeetCode
  3. Extra Characters in a StringMediumLeetCode
  4. Search Suggestions SystemMediumLeetCode
  5. Word Search IIHardLeetCode
BST0/6

Pattern lesson: Binary Search Trees: Ordering, Validation, Insert and Delete

  1. Convert Sorted Array to BSTEasyLeetCode
  2. Validate Binary Search TreeMediumLeetCode
  3. Kth Smallest Element in a BSTMediumLeetCode
  4. Lowest Common Ancestor of a BSTMediumLeetCode
  5. Insert into a BSTMediumLeetCode
  6. Delete Node in a BSTMediumLeetCode
Heap0/18

Pattern lesson: Heaps and Priority Queues: Top-K, Scheduling and Running Medians

Top K Elements11

  1. Kth Largest Element in a StreamEasyLeetCode
  2. Last Stone WeightEasyLeetCode
  3. Top K Frequent ElementsMediumLeetCode
  4. K Closest Points to OriginMediumLeetCode
  5. Kth Largest Element in an ArrayMediumLeetCode
  6. Task SchedulerMediumLeetCode
  7. Min Cost to Connect RopesMediumGeeksforGeeks
  8. Sort Characters By FrequencyMediumLeetCode
  9. Find K Closest ElementsMediumLeetCode
  10. Reorganize StringMediumLeetCode
  11. Maximum Frequency StackHardLeetCode

Two Heaps4

  1. Maximum Sum CombinationMediumGeeksforGeeks
  2. Find Median from Data StreamHardLeetCode
  3. Sliding Window MedianHardLeetCode
  4. IPOHardLeetCode

K-way Merge3

  1. Design TwitterMediumLeetCode
  2. Merge k Sorted ListsHardLeetCode
  3. Smallest Range Covering Elements from K ListsHardLeetCode
Greedy0/17

Pattern lesson: Greedy Algorithms and Intervals: Safe Local Choices and Sweeps

Greedy Choices10

  1. Jump GameMediumLeetCode
  2. Jump Game IIMediumLeetCode
  3. Gas StationMediumLeetCode
  4. Hand of StraightsMediumLeetCode
  5. Merge Triplets to Form TargetMediumLeetCode
  6. Partition LabelsMediumLeetCode
  7. Valid Parenthesis StringMediumLeetCode
  8. Maximum Length of Pair ChainMediumLeetCode
  9. Minimum Add to Make Parentheses ValidMediumLeetCode
  10. Remove Duplicate LettersMediumLeetCode

Intervals7

  1. Meeting RoomsEasyGeeksforGeeks
  2. Merge IntervalsMediumLeetCode
  3. Insert IntervalMediumLeetCode
  4. Non-overlapping IntervalsMediumLeetCode
  5. Interval List IntersectionsMediumLeetCode
  6. Meeting Rooms IIMediumGeeksforGeeks
  7. My Calendar IMediumLeetCode
Backtracking0/12

Pattern lesson: Backtracking: Subsets, Combinations, Permutations and Grid Search

Subsets and Permutations6

  1. Generate ParenthesesMediumLeetCode
  2. SubsetsMediumLeetCode
  3. PermutationsMediumLeetCode
  4. Subsets IIMediumLeetCode
  5. Letter Combinations of a Phone NumberMediumLeetCode
  6. Letter Case PermutationMediumLeetCode

Combinations and Search6

  1. Combination SumMediumLeetCode
  2. Combination Sum IIMediumLeetCode
  3. Word SearchMediumLeetCode
  4. Palindrome PartitioningMediumLeetCode
  5. N-QueensHardLeetCode
  6. Sudoku SolverHardLeetCode
Graph0/27

Pattern lesson: Graphs: BFS, DFS, Topological Sort, Union-Find and Shortest Paths

Graph Traversal5

  1. Find if Path Exists in GraphEasyLeetCode
  2. Clone GraphMediumLeetCode
  3. Number of ProvincesMediumLeetCode
  4. Word LadderHardLeetCode
  5. Reconstruct ItineraryHardLeetCode

Islands (Matrix Traversal)8

  1. Flood FillEasyLeetCode
  2. Island PerimeterEasyLeetCode
  3. Number of IslandsMediumLeetCode
  4. Max Area of IslandMediumLeetCode
  5. Pacific Atlantic Water FlowMediumLeetCode
  6. Surrounded RegionsMediumLeetCode
  7. Rotting OrangesMediumLeetCode
  8. Number of Closed IslandsMediumLeetCode

Topological Sort5

  1. Course ScheduleMediumLeetCode
  2. Course Schedule IIMediumLeetCode
  3. Topological SortMediumGeeksforGeeks
  4. Minimum Height TreesMediumLeetCode
  5. Alien DictionaryHardGeeksforGeeks

Union Find5

  1. Graph Valid TreeMediumGeeksforGeeks
  2. Number of Connected Components in an Undirected Graph with Union-FindMediumGeeksforGeeks
  3. Redundant ConnectionMediumLeetCode
  4. Is Graph Bipartite?MediumLeetCode
  5. Path With Minimum EffortMediumLeetCode

Shortest Paths and MST4

  1. Network Delay TimeMediumLeetCode
  2. Cheapest Flights Within K StopsMediumLeetCode
  3. Min Cost to Connect All PointsMediumLeetCode
  4. Swim in Rising WaterHardLeetCode
Dynamic Programming0/24

Pattern lesson: Dynamic Programming: States, Transitions and the Classic DP Families

1D DP9

  1. Climbing StairsEasyLeetCode
  2. Min Cost Climbing StairsEasyLeetCode
  3. House RobberMediumLeetCode
  4. House Robber IIMediumLeetCode
  5. Decode WaysMediumLeetCode
  6. Coin ChangeMediumLeetCode
  7. Word BreakMediumLeetCode
  8. Longest Increasing SubsequenceMediumLeetCode
  9. Best Time to Buy and Sell Stock with CooldownMediumLeetCode

Knapsack7

  1. Partition Equal Subset SumMediumLeetCode
  2. Coin Change IIMediumLeetCode
  3. Target SumMediumLeetCode
  4. 0 - 1 Knapsack ProblemMediumGeeksforGeeks
  5. Subset Sum ProblemMediumGeeksforGeeks
  6. Count Subsets with SumMediumGeeksforGeeks
  7. Partition Into 2 Subsets with Min Sum DiffHardGeeksforGeeks

2D DP: Strings and Grids8

  1. Longest Palindromic SubstringMediumLeetCode
  2. Palindromic SubstringsMediumLeetCode
  3. Unique PathsMediumLeetCode
  4. Longest Common SubsequenceMediumLeetCode
  5. Interleaving StringMediumLeetCode
  6. Edit DistanceMediumLeetCode
  7. Burst BalloonsHardLeetCode
  8. Regular Expression MatchingHardLeetCode

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Lessons

Work through the lessons in order. Completed lessons show a tick; lessons you have opened are outlined.

Start here

The complete overview of the course in one read.

  1. Data Structures and Algorithms for Data Engineers: How to PrepareBig-O, a repeatable method for coding rounds, the Python built-ins that solve most problems, and a study plan for the 157 practice problems in the planner.Beginner19 min

Beginner

Core concepts you will use every day.

  1. Arrays and Hashing: Sets, Hash Maps, Prefix Sums and IntervalsThe most common coding-interview pattern: seen sets, value-to-index maps, counting, prefix sums, Kadane, intervals, matrices and bit tricks, with tested Python.Beginner25 min
  2. Strings for Coding Interviews: Immutability, Scanning and ParsingHow Python strings work, the scanning and parsing templates behind string problems, and how they map to cleaning keys and parsing messy fields in pipelines.Beginner9 min
  3. Two Pointers: Converging, Read-Write and Partitioning TemplatesUse two indices to replace nested loops: converging pointers on sorted data, read-write compaction, three-way partitioning, and the sort-merge join behind them.Beginner12 min
  4. Queues: FIFO Buffers, Ring Buffers and Queue Design ProblemsHow queues work, deque versus list, building queues from stacks and a ring buffer, time-window counters, and the buffering ideas behind message queues and Kafka.Beginner11 min

Intermediate

Patterns used in production pipelines.

  1. Sliding Window: Fixed, Variable and Monotonic-Deque TemplatesSolve contiguous subarray and substring problems in one pass with fixed and variable windows and a monotonic deque, and see how they power streaming metrics.Intermediate13 min
  2. Stacks: Matching, Evaluation and Monotonic Stack TemplatesUse Python lists as stacks for bracket matching, expression evaluation, min-tracking and monotonic stacks, with tested code and the pipeline jobs they map to.Intermediate12 min
  3. Binary Search: Exact Match, Boundaries and Searching the AnswerOne reliable binary search template for exact matches, first and last positions, rotated arrays and searching on the answer, plus as-of lookups and partition pruning.Intermediate13 min
  4. Linked Lists: Pointer Rewiring, Fast and Slow Pointers, LRU CacheReverse, merge, split and reorder linked lists safely with dummy nodes and fast and slow pointers, then build an LRU cache and a k-way merge in Python.Intermediate20 min
  5. Binary Trees and Tries: DFS, BFS and Prefix Search TemplatesTraverse binary trees with recursive and iterative DFS and level-order BFS, return values up the tree, build and serialise trees, and use tries for prefix search.Intermediate21 min
  6. Binary Search Trees: Ordering, Validation, Insert and DeleteUse the BST ordering rule to search, validate, insert, delete and find the k-th smallest value, and see how the same idea underlies B-tree indexes and range scans.Intermediate13 min
  7. Heaps and Priority Queues: Top-K, Scheduling and Running MediansUse Python's heapq for top-K, k-th largest, k-way merges, task scheduling and running medians, with the bounded-memory streaming patterns Data Engineers rely on.Intermediate18 min
  8. Greedy Algorithms and Intervals: Safe Local Choices and SweepsWhen a locally best choice is provably safe: reach, gas station, grouping and partition problems, plus interval sweeps used for sessionisation and time ranges.Intermediate16 min

Advanced

Performance, internals and edge cases.

  1. Backtracking: Subsets, Combinations, Permutations and Grid SearchOne choose-explore-unchoose template for subsets, combinations, permutations, partitions, word search and N-Queens, with duplicate handling, pruning and itertools.Advanced17 min
  2. Graphs: BFS, DFS, Topological Sort, Union-Find and Shortest PathsModel problems as graphs and solve them with grid DFS and BFS, topological sort for DAG dependencies, union-find, Dijkstra, Bellman-Ford and minimum spanning trees.Advanced29 min
  3. Dynamic Programming: States, Transitions and the Classic DP FamiliesA repeatable method for dynamic programming: define the state and transition, pick memoisation or a table, then solve 1D, grid, string and knapsack problems.Advanced27 min

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