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All Data Engineering interview questions

186 questions across 11 topics. Filter the list, open a question, and tick it off when you can answer it.

#QuestionTopicDifficultyTypeDone
1How should Airflow retries and idempotency work together?AirflowMediumconceptual, scenario
2ETL vs ELT: what factors decide the choice?Data EngineeringEasyconceptual, architecture
3Data lake vs warehouse vs lakehouse: when would you choose each?Data EngineeringMediumconceptual, architecture
4How would you design an idempotent batch pipeline?Data EngineeringMediumarchitecture, scenario
5How would you investigate a suddenly slower data pipeline?Data EngineeringMediumdebugging, scenario
6What are the most important data-quality checks in production?Data EngineeringMediumconceptual, scenario
7How would you design a CDC pipeline?Data EngineeringHardarchitecture, scenario
8What is Unity Catalog used for?DatabricksEasyconceptual
9What problems does Delta Lake solve?Delta LakeEasyconceptual
10What is schema evolution and when is it safe?Delta LakeMediumconceptual, scenario
11Balanced Binary Tree: Height Check with Early ExitDSAEasycoding
12Best Time to Buy and Sell Stock: Maximum Profit From One TradeDSAEasycoding
13Binary Search: Find a Target in a Sorted Array in O(log n)DSAEasycoding
14Climbing Stairs: Count Ways with a Fibonacci-Style DPDSAEasycoding
15Contains Duplicate: Detect Whether Any Value Appears TwiceDSAEasycoding
16Convert Sorted Array to BST: Pick the Middle, Recurse on HalvesDSAEasycoding
17Diameter of Binary Tree: Longest Path via Post-Order HeightsDSAEasycoding
18Implement Queue using Stacks: FIFO With Two Stacks in Amortised O(1)DSAEasycoding
19Implement Stack using Queues: LIFO Behaviour From FIFO PartsDSAEasycoding
20Invert Binary Tree: Recursive and Iterative Mirror SolutionsDSAEasycoding
21Kth Largest Element in a Stream: Size-k Min-HeapDSAEasycoding
22Last Stone Weight: Simulating Smashes with a Max-HeapDSAEasycoding
23Linked List Cycle: Floyd's Fast and Slow PointersDSAEasycoding
24Longest Common Prefix: Shared Start of a List of StringsDSAEasycoding
25Majority Element: Find the Value That Fills More Than Half the ArrayDSAEasycoding
26Maximum Average Subarray I: Best Average Over a Fixed-Length WindowDSAEasycoding
27Maximum Depth of Binary Tree: Recursive DFS, Iterative DFS and BFSDSAEasycoding
28Merge Two Sorted Lists: Dummy Head Iteration and RecursionDSAEasycoding
29Min Cost Climbing Stairs: Cheapest Path to the Top with 1D DPDSAEasycoding
30Move Zeroes: Shift Zeros to the End While Keeping OrderDSAEasycoding
31Next Greater Element I: First Larger Value to the RightDSAEasycoding
32Number of 1 Bits: Count Set Bits in an IntegerDSAEasycoding
33Number of Recent Calls: Count Requests in a Sliding Time WindowDSAEasycoding
34Reverse Bits: Mirror the 32 Bits of an Unsigned IntegerDSAEasycoding
35Reverse Linked List: Iterative and Recursive SolutionsDSAEasycoding
36Reverse String: Reverse a Character Array in PlaceDSAEasycoding
37Same Tree: Comparing Two Binary Trees Recursively and IterativelyDSAEasycoding
38Single Number: Find the Value That Appears Only Once Using XORDSAEasycoding
39Subtree of Another Tree: Brute-Force Matching and Linear SerialisationDSAEasycoding
40Two Sum: Find Two Indices That Add Up to a TargetDSAEasycoding
41Valid Anagram: Check Whether Two Strings Use the Same LettersDSAEasycoding
42Valid Palindrome II: Palindrome After Deleting at Most One CharacterDSAEasycoding
43Valid Palindrome: Check a Phrase While Ignoring Case and PunctuationDSAEasycoding
44Valid Parentheses: Check That Every Bracket Closes in the Right OrderDSAEasycoding
453Sum: Find All Unique Triplets That Sum to ZeroDSAMediumcoding
46Add Two Numbers: Digit-by-Digit Addition on Linked ListsDSAMediumcoding
47Best Time to Buy and Sell Stock with Cooldown: State-Machine DPDSAMediumcoding
48Binary Tree Level Order Traversal: BFS with a Queue, Level by LevelDSAMediumcoding
49Binary Tree Right Side View: Last Node of Each LevelDSAMediumcoding
50Car Fleet: Count the Groups of Cars Arriving at a DestinationDSAMediumcoding
51Cheapest Flights Within K Stops: Bounded Bellman-Ford for Limited HopsDSAMediumcoding
52Clone Graph: Deep-Copy a Connected Graph with a Hash Map and BFS or DFSDSAMediumcoding
53Coin Change II: Count Combinations That Make an AmountDSAMediumcoding
54Coin Change: Fewest Coins with Bottom-Up DPDSAMediumcoding
55Combination Sum II: Use Each Value Once and Avoid Duplicate AnswersDSAMediumcoding
56Combination Sum: Reach a Target with Reusable Values via BacktrackingDSAMediumcoding
57Construct Binary Tree from Preorder and Inorder TraversalDSAMediumcoding
58Container With Most Water: Maximise Area Between Two LinesDSAMediumcoding
59Copy List with Random Pointer: Hash Map and Interleaving SolutionsDSAMediumcoding
60Count Good Nodes in Binary Tree: DFS Carrying the Path MaximumDSAMediumcoding
61Course Schedule II: Return a Valid Course Order with Topological SortDSAMediumcoding
62Course Schedule: Detect a Cycle in a Prerequisite Graph with Kahn's AlgorithmDSAMediumcoding
63Daily Temperatures: Days Until a Warmer Day With a Monotonic StackDSAMediumcoding
64Decode Ways: Count Digit-to-Letter Decodings with Prefix DPDSAMediumcoding
65Delete Node in a BST: Leaf, One Child and Two Children CasesDSAMediumcoding
66Design Add and Search Words: Trie Search with WildcardsDSAMediumcoding, architecture
67Design Circular Queue: A Fixed-Capacity Ring BufferDSAMediumcoding
68Design Twitter: News Feed with a K-Way Heap MergeDSAMediumcoding, architecture
69Edit Distance: Levenshtein Distance with a 2D DP TableDSAMediumcoding
70Encode and Decode Strings: Serialise a List of Strings SafelyDSAMediumcoding
71Evaluate Reverse Polish Notation: Compute a Postfix ExpressionDSAMediumcoding
72Find First and Last Position of a Value: Lower and Upper Bound Binary SearchDSAMediumcoding
73Find Minimum in Rotated Sorted Array: Binary Search Against the Right EndDSAMediumcoding
74Find the Duplicate Number: Cycle Detection on an ArrayDSAMediumcoding
75Generate Parentheses: List Every Balanced String of n PairsDSAMediumcoding
76Graph Valid Tree: Check Edge Count, Connectivity and Cycles with Union-FindDSAMediumcoding
77Group Anagrams: Bucket Words That Share the Same LettersDSAMediumcoding
78House Robber II: Non-Adjacent Maximum Sum When Houses Form a CircleDSAMediumcoding
79House Robber: Maximum Non-Adjacent Sum with Take-or-Skip DPDSAMediumcoding
80Implement Trie (Prefix Tree): Insert, Search and Prefix LookupDSAMediumcoding, architecture
81Insert Interval: Add a Range to a Sorted List and Merge OverlapsDSAMediumcoding
82Insert into a BST: Walk Down to the Empty SpotDSAMediumcoding
83Interleaving String: Can Two Strings Merge into a Third? 2D DPDSAMediumcoding
84K Closest Points to Origin: Bounded Max-Heap and QuickselectDSAMediumcoding
85Koko Eating Bananas: Binary Search on the AnswerDSAMediumcoding
86Kth Largest Element in an Array: Heap, Quickselect and CountingDSAMediumcoding
87Kth Smallest Element in a BST: Inorder Traversal with Early StopDSAMediumcoding
88Letter Combinations of a Phone Number: Cartesian Product by BacktrackingDSAMediumcoding
89Longest Common Subsequence: The Classic Two-String DP TableDSAMediumcoding
90Longest Consecutive Sequence: Longest Run of Consecutive Integers in O(n)DSAMediumcoding
91Longest Increasing Subsequence: O(n^2) DP and O(n log n) Patience SortingDSAMediumcoding
92Longest Palindromic Substring: Expand Around Centres or Interval DPDSAMediumcoding
93Longest Repeating Character Replacement: Window With At Most k ChangesDSAMediumcoding
94Longest Substring Without Repeating Characters: Sliding WindowDSAMediumcoding
95Lowest Common Ancestor of a Binary Tree: One Post-Order SearchDSAMediumcoding
96Lowest Common Ancestor of a BST: Follow the Split PointDSAMediumcoding
97LRU Cache: Hash Map Plus Doubly Linked List for O(1) OperationsDSAMediumcoding, architecture
98Max Area of Island: Largest Connected Land Region with Flood FillDSAMediumcoding
99Maximum Product Subarray: Track Both the Largest and Smallest ProductDSAMediumcoding
100Maximum Subarray: Largest Sum of a Contiguous Slice with Kadane's AlgorithmDSAMediumcoding
101Merge Intervals: Combine Every Overlapping RangeDSAMediumcoding
102Min Cost to Connect All Points: Minimum Spanning Tree with Prim or KruskalDSAMediumcoding
103Min Stack: A Stack That Returns Its Minimum in Constant TimeDSAMediumcoding
104Network Delay Time: Single-Source Shortest Paths with Dijkstra's AlgorithmDSAMediumcoding
105Non-overlapping Intervals: Fewest Removals to Eliminate OverlapsDSAMediumcoding
106Number of Connected Components in an Undirected Graph with Union-FindDSAMediumcoding
107Number of Islands: Count Connected Land Cells with BFS, DFS or Union-FindDSAMediumcoding
108Pacific Atlantic Water Flow: Reverse Multi-Source BFS from Both OceansDSAMediumcoding
109Palindrome Partitioning: Split a String into Palindromes by BacktrackingDSAMediumcoding
110Palindromic Substrings: Count Every Palindrome by Expanding Around CentresDSAMediumcoding
111Partition Equal Subset Sum: 0/1 Knapsack on Half the TotalDSAMediumcoding
112Permutation in String: Does One String Contain a Rearrangement of Another?DSAMediumcoding
113Permutations: Every Ordering of Distinct Values with BacktrackingDSAMediumcoding
114Product of Array Except Self: Prefix and Suffix Products Without DivisionDSAMediumcoding
115Redundant Connection: Find the Edge That Closes a Cycle with Union-FindDSAMediumcoding
116Remove Nth Node From End of List: One Pass with a Gap of nDSAMediumcoding
117Reorder List: Find the Middle, Reverse, Then InterleaveDSAMediumcoding
118Rotate Image: Turn a Square Matrix 90 Degrees Clockwise in PlaceDSAMediumcoding
119Rotting Oranges: Minutes to Spread via Level-by-Level Multi-Source BFSDSAMediumcoding
120Search a 2D Matrix: Binary Search over a Flattened Sorted GridDSAMediumcoding
121Search in Rotated Sorted Array: One-Pass Binary SearchDSAMediumcoding
122Set Matrix Zeroes: Zero Out Rows and Columns in PlaceDSAMediumcoding
123Sort Colors: One-Pass Three-Way Partition of 0s, 1s and 2sDSAMediumcoding
124Spiral Matrix: Read a Grid in Clockwise Spiral OrderDSAMediumcoding
125String to Integer (atoi): Parse a Signed 32-bit Integer by HandDSAMediumcoding
126Subarray Sum Equals K: Count Contiguous Slices With a Given SumDSAMediumcoding
127Subsets II: Power Set Without Duplicates When Values RepeatDSAMediumcoding
128Subsets: Generate the Power Set with Include/Exclude BacktrackingDSAMediumcoding
129Surrounded Regions: Capture Enclosed Cells by Flood-Filling from the BorderDSAMediumcoding
130Target Sum: Count Sign Assignments with Subset-Sum DPDSAMediumcoding
131Task Scheduler: Cooldowns with a Max-Heap or a Counting FormulaDSAMediumcoding
132Time Based Key-Value Store: Versioned Lookups with Binary SearchDSAMediumcoding, architecture
133Top K Frequent Elements: Return the k Most Common ValuesDSAMediumcoding
134Two Sum II: Find a Pair With a Target Sum in a Sorted ArrayDSAMediumcoding
135Unique Paths: Count Grid Routes with 2D DP or a Binomial CoefficientDSAMediumcoding
136Valid Sudoku: Check Rows, Columns and Boxes for Repeated DigitsDSAMediumcoding
137Validate Binary Search Tree: Bounds Recursion and Inorder CheckDSAMediumcoding
138Word Break: Can a String Be Split into Dictionary Words? Prefix DPDSAMediumcoding
139Word Search: Trace a Word Through a Letter Grid with DFS BacktrackingDSAMediumcoding
140Alien Dictionary: Derive a Letter Order from Sorted Words with Topological SortDSAHardcoding
141Binary Tree Maximum Path Sum: Post-Order Gains with a Global BestDSAHardcoding
142Burst Balloons: Interval DP by Choosing the Last Balloon to BurstDSAHardcoding
143Find Median from Data Stream: Two Heaps Kept in BalanceDSAHardcoding
144Largest Rectangle in Histogram: Biggest Area Under the BarsDSAHardcoding
145Median of Two Sorted Arrays: Partition Binary Search in O(log min(m, n))DSAHardcoding
146Merge k Sorted Lists: Min-Heap and Divide-and-Conquer SolutionsDSAHardcoding
147Minimum Window Substring: Shortest Slice Containing Every Required CharacterDSAHardcoding
148N-Queens: Place Non-Attacking Queens Row by Row with BacktrackingDSAHardcoding
149Reconstruct Itinerary: Eulerian Path with Hierholzer's AlgorithmDSAHardcoding
150Regular Expression Matching: Dot and Star with a 2D DP TableDSAHardcoding
151Reverse Nodes in k-Group: In-Place Group Reversal on a Linked ListDSAHardcoding
152Serialize and Deserialize Binary Tree: Preorder with Null MarkersDSAHardcoding
153Sliding Window Maximum: Max of Every Window With a Monotonic DequeDSAHardcoding
154Swim in Rising Water: Minimax Path with a Modified DijkstraDSAHardcoding
155Trapping Rain Water: Total Water Held Between Elevation BarsDSAHardcoding
156Word Ladder: Shortest Word Transformation with BFS and Wildcard BucketsDSAHardcoding
157Word Search II: Find Many Words in a Grid with a Trie and BacktrackingDSAHardcoding
158Explain Kafka partitions and consumer groups.KafkaMediumconceptual, architecture
159What is at-least-once delivery and what problems can it create?KafkaMediumconceptual, scenario
160When should you avoid Python UDFs in PySpark?PySparkMediumconceptual, optimization
161When would you use a broadcast join in Spark?PySparkMediumconceptual, optimization
162Explain shallow copy vs deep copy.PythonEasyconceptual, debugging
163List vs tuple vs set: when would you use each in a data pipeline?PythonEasyconceptual
164What is a generator and why can it help with large datasets?PythonEasyconceptual, coding
165How should exceptions be handled in production data pipelines?PythonMediumconceptual, scenario
166What are Snowflake virtual warehouses?SnowflakeEasyconceptual
167How do micro-partitions affect Snowflake query performance?SnowflakeMediumconceptual, optimization
168What is the difference between a transformation and an action in Spark?Apache SparkEasyconceptual
169Explain Spark jobs, stages and tasks.Apache SparkMediumconceptual
170How does partition count affect Spark performance?Apache SparkMediumoptimization, conceptual
171What causes a shuffle in Spark?Apache SparkMediumconceptual
172What is data skew and how can you mitigate it?Apache SparkHardoptimization, debugging
173Explain INNER JOIN vs LEFT JOIN with a practical example.SQLEasyconceptual, coding
174How do window functions differ from GROUP BY?SQLEasyconceptual, coding
175Average Order Value: SQL Case Study with 8 ApproachesSQLMediumcoding, optimization, scenario
176Customer Lifetime Value: SQL Case Study with 8 ApproachesSQLMediumcoding, optimization, scenario
177Daily Active Users: SQL Case Study with 8 ApproachesSQLMediumcoding, optimization, scenario
178Find the second-highest salary without using a simple MAX approach.SQLMediumcoding
179How would you detect and remove duplicate records safely?SQLMediumcoding, scenario
180New vs Returning Customers: SQL Case Study with 8 ApproachesSQLMediumcoding, optimization, scenario
181Top Selling Products: SQL Case Study with 8 ApproachesSQLMediumcoding, optimization, scenario
182Churn Rate: SQL Case Study with 8 ApproachesSQLHardcoding, optimization, scenario
183Conversion Funnel: SQL Case Study with 8 ApproachesSQLHardcoding, optimization, scenario
184How would you optimize a slow analytical SQL query?SQLHardoptimization, scenario
185Inventory Turnover: SQL Case Study with 8 ApproachesSQLHardcoding, optimization, scenario
186Monthly Revenue: SQL Case Study with 8 ApproachesSQLHardcoding, optimization, scenario

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