All Data Engineering interview questions

All interview questions
#	Question	Topic	Difficulty	Type	Practise
1	How should Airflow retries and idempotency work together?	Airflow	Medium	conceptual, scenario	—
2	ETL vs ELT: what factors decide the choice?	Data Engineering	Easy	conceptual, architecture	—
3	Data lake vs warehouse vs lakehouse: when would you choose each?	Data Engineering	Medium	conceptual, architecture	—
4	How would you design an idempotent batch pipeline?	Data Engineering	Medium	architecture, scenario	—
5	How would you investigate a suddenly slower data pipeline?	Data Engineering	Medium	debugging, scenario	—
6	What are the most important data-quality checks in production?	Data Engineering	Medium	conceptual, scenario	—
7	How would you design a CDC pipeline?	Data Engineering	Hard	architecture, scenario	—
8	What is Unity Catalog used for?	Databricks	Easy	conceptual	—
9	What problems does Delta Lake solve?	Delta Lake	Easy	conceptual	—
10	What is schema evolution and when is it safe?	Delta Lake	Medium	conceptual, scenario	—
11	Backspace String Compare: Read Both Strings Backwards With Skip Counters	DSA	Easy	coding	LeetCode (opens in a new tab)
12	Balanced Binary Tree: Height Check with Early Exit	DSA	Easy	coding	LeetCode (opens in a new tab)
13	Best Time to Buy and Sell Stock: Maximum Profit From One Trade	DSA	Easy	coding	LeetCode (opens in a new tab)
14	Binary Search: Find a Target in a Sorted Array in O(log n)	DSA	Easy	coding	LeetCode (opens in a new tab)
15	Ceil in Sorted Array: Lower-Bound Binary Search	DSA	Easy	coding	GeeksforGeeks (opens in a new tab)
16	Climbing Stairs: Count Ways with a Fibonacci-Style DP	DSA	Easy	coding	LeetCode (opens in a new tab)
17	Complement of Base 10 Integer: Flip Bits With an All-Ones Mask	DSA	Easy	coding	LeetCode (opens in a new tab)
18	Contains Duplicate: Detect Whether Any Value Appears Twice	DSA	Easy	coding	LeetCode (opens in a new tab)
19	Convert Sorted Array to BST: Pick the Middle, Recurse on Halves	DSA	Easy	coding	LeetCode (opens in a new tab)
20	Counting Bits: Set-Bit Counts for 0 to n with a One-Line DP	DSA	Easy	coding	LeetCode (opens in a new tab)
21	Diameter of Binary Tree: Longest Path via Post-Order Heights	DSA	Easy	coding	LeetCode (opens in a new tab)
22	Find All Numbers Disappeared in an Array: Cyclic Sort and In-Place Marking	DSA	Easy	coding	LeetCode (opens in a new tab)
23	Find if Path Exists in Graph: Reachability with BFS or Union-Find	DSA	Easy	coding	LeetCode (opens in a new tab)
24	Find Pivot Index: Balance Left and Right Prefix Sums	DSA	Easy	coding	LeetCode (opens in a new tab)
25	Find Rotation Count: The Index of the Minimum Is the Answer	DSA	Easy	coding	GeeksforGeeks (opens in a new tab)
26	First Unique Character in a String: Count, Then Scan Again	DSA	Easy	coding	LeetCode (opens in a new tab)
27	Flood Fill: Repaint a Connected Region with DFS or BFS	DSA	Easy	coding	LeetCode (opens in a new tab)
28	Happy Number: Detect a Cycle in a Digit-Square Sequence	DSA	Easy	coding	LeetCode (opens in a new tab)
29	Implement Queue using Stacks: FIFO With Two Stacks in Amortised O(1)	DSA	Easy	coding	LeetCode (opens in a new tab)
30	Implement Stack using Queues: LIFO Behaviour From FIFO Parts	DSA	Easy	coding	LeetCode (opens in a new tab)
31	Invert Binary Tree: Recursive and Iterative Mirror Solutions	DSA	Easy	coding	LeetCode (opens in a new tab)
32	Island Perimeter: Count Land Edges Without a Traversal	DSA	Easy	coding	LeetCode (opens in a new tab)
33	Kth Largest Element in a Stream: Size-k Min-Heap	DSA	Easy	coding	LeetCode (opens in a new tab)
34	Last Stone Weight: Simulating Smashes with a Max-Heap	DSA	Easy	coding	LeetCode (opens in a new tab)
35	Linked List Cycle: Floyd's Fast and Slow Pointers	DSA	Easy	coding	LeetCode (opens in a new tab)
36	Longest Common Prefix: Shared Start of a List of Strings	DSA	Easy	coding	LeetCode (opens in a new tab)
37	Longest Palindrome: Pair Up Letter Counts and Keep One Centre	DSA	Easy	coding	LeetCode (opens in a new tab)
38	Majority Element: Find the Value That Fills More Than Half the Array	DSA	Easy	coding	LeetCode (opens in a new tab)
39	Max Sum Subarray of Size K: The Fixed-Size Sliding Window	DSA	Easy	coding	GeeksforGeeks (opens in a new tab)
40	Maximum Average Subarray I: Best Average Over a Fixed-Length Window	DSA	Easy	coding	LeetCode (opens in a new tab)
41	Maximum Depth of Binary Tree: Recursive DFS, Iterative DFS and BFS	DSA	Easy	coding	LeetCode (opens in a new tab)
42	Meeting Rooms: Check Whether One Person Can Attend Every Meeting	DSA	Easy	coding	GeeksforGeeks (opens in a new tab)
43	Merge Two Sorted Lists: Dummy Head Iteration and Recursion	DSA	Easy	coding	LeetCode (opens in a new tab)
44	Middle of the Linked List: Find It in One Pass With Fast and Slow Pointers	DSA	Easy	coding	LeetCode (opens in a new tab)
45	Min Cost Climbing Stairs: Cheapest Path to the Top with 1D DP	DSA	Easy	coding	LeetCode (opens in a new tab)
46	Missing Number: Find the One Value Absent From 0 to n	DSA	Easy	coding	LeetCode (opens in a new tab)
47	Move Zeroes: Shift Zeros to the End While Keeping Order	DSA	Easy	coding	LeetCode (opens in a new tab)
48	Next Greater Element I: First Larger Value to the Right	DSA	Easy	coding	LeetCode (opens in a new tab)
49	Number of 1 Bits: Count Set Bits in an Integer	DSA	Easy	coding	LeetCode (opens in a new tab)
50	Number of Recent Calls: Count Requests in a Sliding Time Window	DSA	Easy	coding	LeetCode (opens in a new tab)
51	Palindrome Linked List: Find the Middle, Reverse the Back Half, Compare	DSA	Easy	coding	LeetCode (opens in a new tab)
52	Ransom Note: Check Letter Supply Against Demand With a Counter	DSA	Easy	coding	LeetCode (opens in a new tab)
53	Remove All Adjacent Duplicates In String: Cancel Pairs With a Stack	DSA	Easy	coding	LeetCode (opens in a new tab)
54	Remove Duplicates from Sorted Array: Compact Unique Values In Place	DSA	Easy	coding	LeetCode (opens in a new tab)
55	Reverse Bits: Mirror the 32 Bits of an Unsigned Integer	DSA	Easy	coding	LeetCode (opens in a new tab)
56	Reverse Linked List: Iterative and Recursive Solutions	DSA	Easy	coding	LeetCode (opens in a new tab)
57	Reverse String: Reverse a Character Array in Place	DSA	Easy	coding	LeetCode (opens in a new tab)
58	Same Tree: Comparing Two Binary Trees Recursively and Iteratively	DSA	Easy	coding	LeetCode (opens in a new tab)
59	Segregate 0s and 1s: Partition a Binary Array in One Pass	DSA	Easy	coding	GeeksforGeeks (opens in a new tab)
60	Set Mismatch: Find the Duplicate and the Missing Number With Cyclic Sort	DSA	Easy	coding	LeetCode (opens in a new tab)
61	Single Number: Find the Value That Appears Only Once Using XOR	DSA	Easy	coding	LeetCode (opens in a new tab)
62	Squares of a Sorted Array: Merge From Both Ends Without Sorting	DSA	Easy	coding	LeetCode (opens in a new tab)
63	Subtree of Another Tree: Brute-Force Matching and Linear Serialisation	DSA	Easy	coding	LeetCode (opens in a new tab)
64	Two Sum: Find Two Indices That Add Up to a Target	DSA	Easy	coding	LeetCode (opens in a new tab)
65	Valid Anagram: Check Whether Two Strings Use the Same Letters	DSA	Easy	coding	LeetCode (opens in a new tab)
66	Valid Palindrome II: Palindrome After Deleting at Most One Character	DSA	Easy	coding	LeetCode (opens in a new tab)
67	Valid Palindrome: Check a Phrase While Ignoring Case and Punctuation	DSA	Easy	coding	LeetCode (opens in a new tab)
68	Valid Parentheses: Check That Every Bracket Closes in the Right Order	DSA	Easy	coding	LeetCode (opens in a new tab)
69	0 - 1 Knapsack Problem: Take or Skip Each Item Once	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
70	132 Pattern: Find a Low, High, Middle Subsequence in One Pass	DSA	Medium	coding	LeetCode (opens in a new tab)
71	3Sum Closest: Sort, Fix One Value, and Squeeze Two Pointers	DSA	Medium	coding	LeetCode (opens in a new tab)
72	3Sum: Find All Unique Triplets That Sum to Zero	DSA	Medium	coding	LeetCode (opens in a new tab)
73	4Sum: Two Fixed Indices, Two Pointers and Careful Duplicate Skipping	DSA	Medium	coding	LeetCode (opens in a new tab)
74	Add Two Numbers: Digit-by-Digit Addition on Linked Lists	DSA	Medium	coding	LeetCode (opens in a new tab)
75	Aggressive Cows: Maximise the Minimum Gap with Binary Search	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
76	Best Time to Buy and Sell Stock with Cooldown: State-Machine DP	DSA	Medium	coding	LeetCode (opens in a new tab)
77	Binary Tree Level Order Traversal: BFS with a Queue, Level by Level	DSA	Medium	coding	LeetCode (opens in a new tab)
78	Binary Tree Right Side View: Last Node of Each Level	DSA	Medium	coding	LeetCode (opens in a new tab)
79	Capacity To Ship Packages Within D Days: Binary Search on Capacity	DSA	Medium	coding	LeetCode (opens in a new tab)
80	Car Fleet: Count the Groups of Cars Arriving at a Destination	DSA	Medium	coding	LeetCode (opens in a new tab)
81	Cheapest Flights Within K Stops: Bounded Bellman-Ford for Limited Hops	DSA	Medium	coding	LeetCode (opens in a new tab)
82	Circular Array Loop: Fast and Slow Pointers on Index Jumps	DSA	Medium	coding	LeetCode (opens in a new tab)
83	Clone Graph: Deep-Copy a Connected Graph with a Hash Map and BFS or DFS	DSA	Medium	coding	LeetCode (opens in a new tab)
84	Coin Change II: Count Combinations That Make an Amount	DSA	Medium	coding	LeetCode (opens in a new tab)
85	Coin Change: Fewest Coins with Bottom-Up DP	DSA	Medium	coding	LeetCode (opens in a new tab)
86	Combination Sum II: Use Each Value Once and Avoid Duplicate Answers	DSA	Medium	coding	LeetCode (opens in a new tab)
87	Combination Sum: Reach a Target with Reusable Values via Backtracking	DSA	Medium	coding	LeetCode (opens in a new tab)
88	Construct Binary Tree from Preorder and Inorder Traversal	DSA	Medium	coding	LeetCode (opens in a new tab)
89	Container With Most Water: Maximise Area Between Two Lines	DSA	Medium	coding	LeetCode (opens in a new tab)
90	Contiguous Array: Longest Balanced 0/1 Subarray via Prefix Sums	DSA	Medium	coding	LeetCode (opens in a new tab)
91	Copy List with Random Pointer: Hash Map and Interleaving Solutions	DSA	Medium	coding	LeetCode (opens in a new tab)
92	Count Good Nodes in Binary Tree: DFS Carrying the Path Maximum	DSA	Medium	coding	LeetCode (opens in a new tab)
93	Count Subsets with Sum: Add Up the Ways, Not Just True or False	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
94	Course Schedule II: Return a Valid Course Order with Topological Sort	DSA	Medium	coding	LeetCode (opens in a new tab)
95	Course Schedule: Detect a Cycle in a Prerequisite Graph with Kahn's Algorithm	DSA	Medium	coding	LeetCode (opens in a new tab)
96	Daily Temperatures: Days Until a Warmer Day With a Monotonic Stack	DSA	Medium	coding	LeetCode (opens in a new tab)
97	Decode Ways: Count Digit-to-Letter Decodings with Prefix DP	DSA	Medium	coding	LeetCode (opens in a new tab)
98	Delete Node in a BST: Leaf, One Child and Two Children Cases	DSA	Medium	coding	LeetCode (opens in a new tab)
99	Design Add and Search Words: Trie Search with Wildcards	DSA	Medium	coding, architecture	LeetCode (opens in a new tab)
100	Design Circular Queue: A Fixed-Capacity Ring Buffer	DSA	Medium	coding	LeetCode (opens in a new tab)
101	Design Twitter: News Feed with a K-Way Heap Merge	DSA	Medium	coding, architecture	LeetCode (opens in a new tab)
102	Edit Distance: Levenshtein Distance with a 2D DP Table	DSA	Medium	coding	LeetCode (opens in a new tab)
103	Encode and Decode Strings: Serialise a List of Strings Safely	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
104	Evaluate Reverse Polish Notation: Compute a Postfix Expression	DSA	Medium	coding	LeetCode (opens in a new tab)
105	Extra Characters in a String: Dynamic Programming over a Trie of Words	DSA	Medium	coding	LeetCode (opens in a new tab)
106	Find All Anagrams in a String: Fixed Window With Letter Counts	DSA	Medium	coding	LeetCode (opens in a new tab)
107	Find All Duplicates in an Array: Cyclic Sort and Sign Marking in O(1) Space	DSA	Medium	coding	LeetCode (opens in a new tab)
108	Find First and Last Position of a Value: Lower and Upper Bound Binary Search	DSA	Medium	coding	LeetCode (opens in a new tab)
109	Find K Closest Elements: Binary Search for the Best Window	DSA	Medium	coding	LeetCode (opens in a new tab)
110	Find Minimum in Rotated Sorted Array: Binary Search Against the Right End	DSA	Medium	coding	LeetCode (opens in a new tab)
111	Find Peak Element: Follow the Uphill Side with Binary Search	DSA	Medium	coding	LeetCode (opens in a new tab)
112	Find the Duplicate Number: Cycle Detection on an Array	DSA	Medium	coding	LeetCode (opens in a new tab)
113	Fruit Into Baskets: Longest Window With at Most Two Distinct Values	DSA	Medium	coding	LeetCode (opens in a new tab)
114	Gas Station: Find the Start of a Circular Route in One Greedy Pass	DSA	Medium	coding	LeetCode (opens in a new tab)
115	Generate Parentheses: List Every Balanced String of n Pairs	DSA	Medium	coding	LeetCode (opens in a new tab)
116	Graph Valid Tree: Check Edge Count, Connectivity and Cycles with Union-Find	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
117	Group Anagrams: Bucket Words That Share the Same Letters	DSA	Medium	coding	LeetCode (opens in a new tab)
118	Hand of Straights: Group Cards into Consecutive Runs Greedily	DSA	Medium	coding	LeetCode (opens in a new tab)
119	House Robber II: Non-Adjacent Maximum Sum When Houses Form a Circle	DSA	Medium	coding	LeetCode (opens in a new tab)
120	House Robber: Maximum Non-Adjacent Sum with Take-or-Skip DP	DSA	Medium	coding	LeetCode (opens in a new tab)
121	Implement Trie (Prefix Tree): Insert, Search and Prefix Lookup	DSA	Medium	coding, architecture	LeetCode (opens in a new tab)
122	Insert Interval: Add a Range to a Sorted List and Merge Overlaps	DSA	Medium	coding	LeetCode (opens in a new tab)
123	Insert into a BST: Walk Down to the Empty Spot	DSA	Medium	coding	LeetCode (opens in a new tab)
124	Interleaving String: Can Two Strings Merge into a Third? 2D DP	DSA	Medium	coding	LeetCode (opens in a new tab)
125	Interval List Intersections: Two Pointers over Sorted Ranges	DSA	Medium	coding	LeetCode (opens in a new tab)
126	Is Graph Bipartite?: Two-Colour Every Component	DSA	Medium	coding	LeetCode (opens in a new tab)
127	Jump Game II: Fewest Jumps to the End with Greedy Level-by-Level BFS	DSA	Medium	coding	LeetCode (opens in a new tab)
128	Jump Game: Can You Reach the Last Index? Greedy Furthest Reach	DSA	Medium	coding	LeetCode (opens in a new tab)
129	K Closest Points to Origin: Bounded Max-Heap and Quickselect	DSA	Medium	coding	LeetCode (opens in a new tab)
130	Koko Eating Bananas: Binary Search on the Answer	DSA	Medium	coding	LeetCode (opens in a new tab)
131	Kth Largest Element in an Array: Heap, Quickselect and Counting	DSA	Medium	coding	LeetCode (opens in a new tab)
132	Kth Smallest Element in a BST: Inorder Traversal with Early Stop	DSA	Medium	coding	LeetCode (opens in a new tab)
133	Kth Smallest Element in a Sorted Matrix: Binary Search on Values	DSA	Medium	coding	LeetCode (opens in a new tab)
134	Letter Case Permutation: Branch Twice on Every Letter	DSA	Medium	coding	LeetCode (opens in a new tab)
135	Letter Combinations of a Phone Number: Cartesian Product by Backtracking	DSA	Medium	coding	LeetCode (opens in a new tab)
136	Linked List Cycle II: Find Where the Cycle Starts With Floyd's Algorithm	DSA	Medium	coding	LeetCode (opens in a new tab)
137	Longest Common Subsequence: The Classic Two-String DP Table	DSA	Medium	coding	LeetCode (opens in a new tab)
138	Longest Consecutive Sequence: Longest Run of Consecutive Integers in O(n)	DSA	Medium	coding	LeetCode (opens in a new tab)
139	Longest Increasing Subsequence: O(n^2) DP and O(n log n) Patience Sorting	DSA	Medium	coding	LeetCode (opens in a new tab)
140	Longest K Unique Characters Substring: A Window Bounded by a Distinct Count	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
141	Longest Palindromic Substring: Expand Around Centres or Interval DP	DSA	Medium	coding	LeetCode (opens in a new tab)
142	Longest Repeating Character Replacement: Window With At Most k Changes	DSA	Medium	coding	LeetCode (opens in a new tab)
143	Longest Substring Without Repeating Characters: Sliding Window	DSA	Medium	coding	LeetCode (opens in a new tab)
144	Lowest Common Ancestor of a Binary Tree: One Post-Order Search	DSA	Medium	coding	LeetCode (opens in a new tab)
145	Lowest Common Ancestor of a BST: Follow the Split Point	DSA	Medium	coding	LeetCode (opens in a new tab)
146	LRU Cache: Hash Map Plus Doubly Linked List for O(1) Operations	DSA	Medium	coding, architecture	LeetCode (opens in a new tab)
147	Max Area of Island: Largest Connected Land Region with Flood Fill	DSA	Medium	coding	LeetCode (opens in a new tab)
148	Max Consecutive Ones III: Longest Window With at Most K Zeros	DSA	Medium	coding	LeetCode (opens in a new tab)
149	Maximum Absolute Sum of Any Subarray: Run Kadane for Max and Min	DSA	Medium	coding	LeetCode (opens in a new tab)
150	Maximum Candies Allocated to K Children: Binary Search on the Share	DSA	Medium	coding	LeetCode (opens in a new tab)
151	Maximum Length of Pair Chain: Greedy by Earliest End	DSA	Medium	coding	LeetCode (opens in a new tab)
152	Maximum Product Subarray: Track Both the Largest and Smallest Product	DSA	Medium	coding	LeetCode (opens in a new tab)
153	Maximum Subarray Sum with One Deletion: Kadane With Two States	DSA	Medium	coding	LeetCode (opens in a new tab)
154	Maximum Subarray: Largest Sum of a Contiguous Slice with Kadane's Algorithm	DSA	Medium	coding	LeetCode (opens in a new tab)
155	Maximum Sum Circular Subarray: Kadane Plus Total Minus Minimum	DSA	Medium	coding	LeetCode (opens in a new tab)
156	Maximum Sum Combination: The K Largest Pair Sums with a Max-Heap	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
157	Meeting Rooms II: Count the Rooms with a Min-Heap or a Sweep Line	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
158	Merge Intervals: Combine Every Overlapping Range	DSA	Medium	coding	LeetCode (opens in a new tab)
159	Merge Triplets to Form Target: Keep Only Triplets That Never Overshoot	DSA	Medium	coding	LeetCode (opens in a new tab)
160	Min Cost to Connect All Points: Minimum Spanning Tree with Prim or Kruskal	DSA	Medium	coding	LeetCode (opens in a new tab)
161	Min Cost to Connect Ropes: Always Join the Two Shortest	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
162	Min Stack: A Stack That Returns Its Minimum in Constant Time	DSA	Medium	coding	LeetCode (opens in a new tab)
163	Minimum Add to Make Parentheses Valid: Count Unmatched Brackets in One Pass	DSA	Medium	coding	LeetCode (opens in a new tab)
164	Minimum Height Trees: Trim Leaves Until the Centre Remains	DSA	Medium	coding	LeetCode (opens in a new tab)
165	Minimum Number of Days to Make m Bouquets: Binary Search on the Day	DSA	Medium	coding	LeetCode (opens in a new tab)
166	Minimum Size Subarray Sum: Grow Until Valid, Then Shrink	DSA	Medium	coding	LeetCode (opens in a new tab)
167	My Calendar I: Accept Bookings Only When They Do Not Overlap	DSA	Medium	coding	LeetCode (opens in a new tab)
168	Network Delay Time: Single-Source Shortest Paths with Dijkstra's Algorithm	DSA	Medium	coding	LeetCode (opens in a new tab)
169	Next Greater Element II: Monotonic Stack Over a Circular Array	DSA	Medium	coding	LeetCode (opens in a new tab)
170	Non-overlapping Intervals: Fewest Removals to Eliminate Overlaps	DSA	Medium	coding	LeetCode (opens in a new tab)
171	Number of Closed Islands: Sink the Border, Then Count	DSA	Medium	coding	LeetCode (opens in a new tab)
172	Number of Connected Components in an Undirected Graph with Union-Find	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
173	Number of Islands: Count Connected Land Cells with BFS, DFS or Union-Find	DSA	Medium	coding	LeetCode (opens in a new tab)
174	Number of Occurrence: Count a Value with Two Boundary Searches	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
175	Number of Provinces: Count Components in an Adjacency Matrix	DSA	Medium	coding	LeetCode (opens in a new tab)
176	Pacific Atlantic Water Flow: Reverse Multi-Source BFS from Both Oceans	DSA	Medium	coding	LeetCode (opens in a new tab)
177	Palindrome Partitioning: Split a String into Palindromes by Backtracking	DSA	Medium	coding	LeetCode (opens in a new tab)
178	Palindromic Substrings: Count Every Palindrome by Expanding Around Centres	DSA	Medium	coding	LeetCode (opens in a new tab)
179	Partition Equal Subset Sum: 0/1 Knapsack on Half the Total	DSA	Medium	coding	LeetCode (opens in a new tab)
180	Partition Labels: Split a String So Each Letter Stays in One Part	DSA	Medium	coding	LeetCode (opens in a new tab)
181	Path With Minimum Effort: Minimise the Largest Step on a Grid	DSA	Medium	coding	LeetCode (opens in a new tab)
182	Peak Index in a Mountain Array: Binary Search on the Slope	DSA	Medium	coding	LeetCode (opens in a new tab)
183	Permutation in String: Does One String Contain a Rearrangement of Another?	DSA	Medium	coding	LeetCode (opens in a new tab)
184	Permutations: Every Ordering of Distinct Values with Backtracking	DSA	Medium	coding	LeetCode (opens in a new tab)
185	Product of Array Except Self: Prefix and Suffix Products Without Division	DSA	Medium	coding	LeetCode (opens in a new tab)
186	Redundant Connection: Find the Edge That Closes a Cycle with Union-Find	DSA	Medium	coding	LeetCode (opens in a new tab)
187	Remove All Adjacent Duplicates in String II: Stack of Character Counts	DSA	Medium	coding	LeetCode (opens in a new tab)
188	Remove Duplicate Letters: Smallest Order with a Greedy Monotonic Stack	DSA	Medium	coding	LeetCode (opens in a new tab)
189	Remove K Digits: Smallest Number With a Greedy Monotonic Stack	DSA	Medium	coding	LeetCode (opens in a new tab)
190	Remove Nodes From Linked List: Keep Nodes With Nothing Larger to Their Right	DSA	Medium	coding	LeetCode (opens in a new tab)
191	Remove Nth Node From End of List: One Pass with a Gap of n	DSA	Medium	coding	LeetCode (opens in a new tab)
192	Reorder List: Find the Middle, Reverse, Then Interleave	DSA	Medium	coding	LeetCode (opens in a new tab)
193	Reorganize String: Place the Most Frequent Character First, Never Twice in a Row	DSA	Medium	coding	LeetCode (opens in a new tab)
194	Reverse Linked List II: Reverse a Sublist in One Pass With a Dummy Node	DSA	Medium	coding	LeetCode (opens in a new tab)
195	Rotate Image: Turn a Square Matrix 90 Degrees Clockwise in Place	DSA	Medium	coding	LeetCode (opens in a new tab)
196	Rotate List: Close the Ring, Then Cut It at the New Tail	DSA	Medium	coding	LeetCode (opens in a new tab)
197	Rotting Oranges: Minutes to Spread via Level-by-Level Multi-Source BFS	DSA	Medium	coding	LeetCode (opens in a new tab)
198	Search a 2D Matrix II: Staircase Search from the Top-Right Corner	DSA	Medium	coding	LeetCode (opens in a new tab)
199	Search a 2D Matrix: Binary Search over a Flattened Sorted Grid	DSA	Medium	coding	LeetCode (opens in a new tab)
200	Search in Rotated Sorted Array: One-Pass Binary Search	DSA	Medium	coding	LeetCode (opens in a new tab)
201	Search Suggestions System: Autocomplete with a Trie or Sorted Binary Search	DSA	Medium	coding	LeetCode (opens in a new tab)
202	Set Matrix Zeroes: Zero Out Rows and Columns in Place	DSA	Medium	coding	LeetCode (opens in a new tab)
203	Shortest Unsorted Continuous Subarray: Find the Boundaries With Running Max and Min	DSA	Medium	coding	LeetCode (opens in a new tab)
204	Simplify Path: Canonical Unix Paths With a Stack of Directory Names	DSA	Medium	coding	LeetCode (opens in a new tab)
205	Single Number III: Split Two Unique Values With One XOR Bit	DSA	Medium	coding	LeetCode (opens in a new tab)
206	Sort Characters By Frequency: Count, Then Order by a Heap or Buckets	DSA	Medium	coding	LeetCode (opens in a new tab)
207	Sort Colors: One-Pass Three-Way Partition of 0s, 1s and 2s	DSA	Medium	coding	LeetCode (opens in a new tab)
208	Spiral Matrix: Read a Grid in Clockwise Spiral Order	DSA	Medium	coding	LeetCode (opens in a new tab)
209	String to Integer (atoi): Parse a Signed 32-bit Integer by Hand	DSA	Medium	coding	LeetCode (opens in a new tab)
210	Subarray Product Less Than K: Count Windows Ending at Each Index	DSA	Medium	coding	LeetCode (opens in a new tab)
211	Subarray Sum Equals K: Count Contiguous Slices With a Given Sum	DSA	Medium	coding	LeetCode (opens in a new tab)
212	Subarray Sums Divisible by K: Count Matching Prefix Remainders	DSA	Medium	coding	LeetCode (opens in a new tab)
213	Subset Sum Problem: Track Every Reachable Total	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
214	Subsets II: Power Set Without Duplicates When Values Repeat	DSA	Medium	coding	LeetCode (opens in a new tab)
215	Subsets: Generate the Power Set with Include/Exclude Backtracking	DSA	Medium	coding	LeetCode (opens in a new tab)
216	Sum of Two Integers: Add Without the Plus or Minus Operator	DSA	Medium	coding	LeetCode (opens in a new tab)
217	Surrounded Regions: Capture Enclosed Cells by Flood-Filling from the Border	DSA	Medium	coding	LeetCode (opens in a new tab)
218	Swap Nodes in Pairs: Rewire Every Two Nodes With a Dummy Head	DSA	Medium	coding	LeetCode (opens in a new tab)
219	Target Sum: Count Sign Assignments with Subset-Sum DP	DSA	Medium	coding	LeetCode (opens in a new tab)
220	Task Scheduler: Cooldowns with a Max-Heap or a Counting Formula	DSA	Medium	coding	LeetCode (opens in a new tab)
221	Time Based Key-Value Store: Versioned Lookups with Binary Search	DSA	Medium	coding, architecture	LeetCode (opens in a new tab)
222	Top K Frequent Elements: Return the k Most Common Values	DSA	Medium	coding	LeetCode (opens in a new tab)
223	Topological Sort: Order a DAG with Kahn's Algorithm or DFS	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
224	Triplets with Smaller Sum: Count Many Pairs at Once With Two Pointers	DSA	Medium	coding	GeeksforGeeks (opens in a new tab)
225	Two Sum II: Find a Pair With a Target Sum in a Sorted Array	DSA	Medium	coding	LeetCode (opens in a new tab)
226	Unique Paths: Count Grid Routes with 2D DP or a Binomial Coefficient	DSA	Medium	coding	LeetCode (opens in a new tab)
227	Valid Parenthesis String: Track a Range of Open Counts Greedily	DSA	Medium	coding	LeetCode (opens in a new tab)
228	Valid Sudoku: Check Rows, Columns and Boxes for Repeated Digits	DSA	Medium	coding	LeetCode (opens in a new tab)
229	Validate Binary Search Tree: Bounds Recursion and Inorder Check	DSA	Medium	coding	LeetCode (opens in a new tab)
230	Word Break: Can a String Be Split into Dictionary Words? Prefix DP	DSA	Medium	coding	LeetCode (opens in a new tab)
231	Word Search: Trace a Word Through a Letter Grid with DFS Backtracking	DSA	Medium	coding	LeetCode (opens in a new tab)
232	Alien Dictionary: Derive a Letter Order from Sorted Words with Topological Sort	DSA	Hard	coding	GeeksforGeeks (opens in a new tab)
233	Binary Tree Maximum Path Sum: Post-Order Gains with a Global Best	DSA	Hard	coding	LeetCode (opens in a new tab)
234	Burst Balloons: Interval DP by Choosing the Last Balloon to Burst	DSA	Hard	coding	LeetCode (opens in a new tab)
235	Find Median from Data Stream: Two Heaps Kept in Balance	DSA	Hard	coding	LeetCode (opens in a new tab)
236	First Missing Positive: Cyclic Sort Into Home Slots in O(n) Time, O(1) Space	DSA	Hard	coding	LeetCode (opens in a new tab)
237	IPO: Maximise Capital by Picking the Best Affordable Project Each Round	DSA	Hard	coding	LeetCode (opens in a new tab)
238	Largest Rectangle in Histogram: Biggest Area Under the Bars	DSA	Hard	coding	LeetCode (opens in a new tab)
239	Maximum Frequency Stack: Pop the Most Frequent Value in O(1)	DSA	Hard	coding, architecture	LeetCode (opens in a new tab)
240	Median of Two Sorted Arrays: Partition Binary Search in O(log min(m, n))	DSA	Hard	coding	LeetCode (opens in a new tab)
241	Merge k Sorted Lists: Min-Heap and Divide-and-Conquer Solutions	DSA	Hard	coding	LeetCode (opens in a new tab)
242	Minimum Window Substring: Shortest Slice Containing Every Required Character	DSA	Hard	coding	LeetCode (opens in a new tab)
243	N-Queens: Place Non-Attacking Queens Row by Row with Backtracking	DSA	Hard	coding	LeetCode (opens in a new tab)
244	Partition Into 2 Subsets with Min Sum Diff: Subset Sum Up to Half the Total	DSA	Hard	coding	GeeksforGeeks (opens in a new tab)
245	Reconstruct Itinerary: Eulerian Path with Hierholzer's Algorithm	DSA	Hard	coding	LeetCode (opens in a new tab)
246	Regular Expression Matching: Dot and Star with a 2D DP Table	DSA	Hard	coding	LeetCode (opens in a new tab)
247	Reverse Nodes in k-Group: In-Place Group Reversal on a Linked List	DSA	Hard	coding	LeetCode (opens in a new tab)
248	Serialize and Deserialize Binary Tree: Preorder with Null Markers	DSA	Hard	coding	LeetCode (opens in a new tab)
249	Shortest Subarray with Sum at Least K: Prefix Sums and a Monotonic Deque	DSA	Hard	coding	LeetCode (opens in a new tab)
250	Sliding Window Maximum: Max of Every Window With a Monotonic Deque	DSA	Hard	coding	LeetCode (opens in a new tab)
251	Sliding Window Median: Two Heaps with Lazy Deletion	DSA	Hard	coding	LeetCode (opens in a new tab)
252	Smallest Range Covering Elements from K Lists: K-Way Merge with a Min-Heap	DSA	Hard	coding	LeetCode (opens in a new tab)
253	Split Array Largest Sum: Binary Search on the Largest Part	DSA	Hard	coding	LeetCode (opens in a new tab)
254	Substring with Concatenation of All Words: Word-Sized Sliding Windows per Offset	DSA	Hard	coding	LeetCode (opens in a new tab)
255	Sudoku Solver: Backtracking with Constraint Sets and Smart Cell Choice	DSA	Hard	coding	LeetCode (opens in a new tab)
256	Swim in Rising Water: Minimax Path with a Modified Dijkstra	DSA	Hard	coding	LeetCode (opens in a new tab)
257	Trapping Rain Water: Total Water Held Between Elevation Bars	DSA	Hard	coding	LeetCode (opens in a new tab)
258	Word Ladder: Shortest Word Transformation with BFS and Wildcard Buckets	DSA	Hard	coding	LeetCode (opens in a new tab)
259	Word Search II: Find Many Words in a Grid with a Trie and Backtracking	DSA	Hard	coding	LeetCode (opens in a new tab)
260	Explain Kafka partitions and consumer groups.	Kafka	Medium	conceptual, architecture	—
261	What is at-least-once delivery and what problems can it create?	Kafka	Medium	conceptual, scenario	—
262	When should you avoid Python UDFs in PySpark?	PySpark	Medium	conceptual, optimization	—
263	When would you use a broadcast join in Spark?	PySpark	Medium	conceptual, optimization	—
264	Explain shallow copy vs deep copy.	Python	Easy	conceptual, debugging	—
265	List vs tuple vs set: when would you use each in a data pipeline?	Python	Easy	conceptual	—
266	What is a generator and why can it help with large datasets?	Python	Easy	conceptual, coding	—
267	How should exceptions be handled in production data pipelines?	Python	Medium	conceptual, scenario	—
268	What are Snowflake virtual warehouses?	Snowflake	Easy	conceptual	—
269	How do micro-partitions affect Snowflake query performance?	Snowflake	Medium	conceptual, optimization	—
270	What is the difference between a transformation and an action in Spark?	Apache Spark	Easy	conceptual	—
271	Explain Spark jobs, stages and tasks.	Apache Spark	Medium	conceptual	—
272	How does partition count affect Spark performance?	Apache Spark	Medium	optimization, conceptual	—
273	What causes a shuffle in Spark?	Apache Spark	Medium	conceptual	—
274	What is data skew and how can you mitigate it?	Apache Spark	Hard	optimization, debugging	—
275	Explain INNER JOIN vs LEFT JOIN with a practical example.	SQL	Easy	conceptual, coding	—
276	How do window functions differ from GROUP BY?	SQL	Easy	conceptual, coding	—
277	Average Order Value: SQL Case Study with 8 Approaches	SQL	Medium	coding, optimization, scenario	—
278	Customer Lifetime Value: SQL Case Study with 8 Approaches	SQL	Medium	coding, optimization, scenario	—
279	Daily Active Users: SQL Case Study with 8 Approaches	SQL	Medium	coding, optimization, scenario	—
280	Find the second-highest salary without using a simple MAX approach.	SQL	Medium	coding	LeetCode (opens in a new tab)
281	How would you detect and remove duplicate records safely?	SQL	Medium	coding, scenario	LeetCode (opens in a new tab)
282	Lead Scoring: SQL Case Study with 7 Approaches	SQL	Medium	coding, scenario, optimization	—
283	New vs Returning Customers: SQL Case Study with 8 Approaches	SQL	Medium	coding, optimization, scenario	—
284	Refund Analysis: SQL Case Study with 7 Approaches	SQL	Medium	coding, optimization, scenario	—
285	Session Duration: SQL Case Study with 8 Approaches	SQL	Medium	coding, optimization, scenario	—
286	Subscription Renewals: SQL Case Study with 7 Approaches	SQL	Medium	coding, optimization, scenario	—
287	Top Selling Products: SQL Case Study with 8 Approaches	SQL	Medium	coding, optimization, scenario	—
288	A/B Test Results: SQL Case Study with 7 Approaches	SQL	Hard	coding, scenario, optimization	—
289	Churn Rate: SQL Case Study with 8 Approaches	SQL	Hard	coding, optimization, scenario	—
290	Conversion Funnel: SQL Case Study with 8 Approaches	SQL	Hard	coding, optimization, scenario	—
291	Employee Hierarchy: SQL Case Study with 8 Approaches	SQL	Hard	coding, optimization, scenario	—
292	Fraud Pattern Detection: SQL Case Study with 8 Approaches	SQL	Hard	coding, optimization, scenario	—
293	How would you optimize a slow analytical SQL query?	SQL	Hard	optimization, scenario	—
294	Inventory Turnover: SQL Case Study with 8 Approaches	SQL	Hard	coding, optimization, scenario	—
295	Monthly Revenue: SQL Case Study with 8 Approaches	SQL	Hard	coding, optimization, scenario	—

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