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Citadel DSA Interview Questions
89 curated coding interview questions directly asked in Citadel technical rounds, sorted by frequency with recency and difficulty diagnostics.
89
Total Questions
6 (7%)
Easy Problems
55 (62%)
Medium Problems
28 (31%)
Hard Problems
🔥 Most Tested Topics:
Core DSA (30)Arrays (20)Strings (11)Design (11)Trees (7)
📂 Sourced Datasets:
Last 3 monthsLast 6 monthsAll questionsOlder than 6 months
| ID | Problem | Difficulty | Topic | Pattern | Acceptance | Frequency | Recency |
|---|---|---|---|---|---|---|---|
| 2050 | Parallel Courses III | Hard | Graphs | BFS / DFS / Topological Sort | 66.8% | 100.0% | 3m |
| 239 | Sliding Window Maximum | Hard | Arrays | Sorting / Prefix / Scan; Sliding Window | 48.8% | 100.0% | all |
| 647 | Palindromic Substrings | Medium | Strings; Trees | Hashing / Sliding Window; DFS / BFS | 72.8% | 100.0% | all |
| 2484 | Count Palindromic Subsequences | Hard | Core DSA | Implementation / Reasoning | 41.2% | 100.0% | all |
| 127 | Word Ladder | Hard | Strings | Hashing / Sliding Window | 45.6% | 87.5% | 3m |
| 295 | Find Median from Data Stream | Hard | Heap | Priority Queue | 54.5% | 87.5% | 3m |
| 1801 | Number of Orders in the Backlog | Medium | Core DSA | Implementation / Reasoning | 54.0% | 87.5% | 6m |
| 348 | Design Tic-Tac-Toe | Medium | Design | Data Structure Design | 58.7% | 87.5% | 6m |
| 121 | Best Time to Buy and Sell Stock | Easy | Core DSA | Implementation / Reasoning | 56.8% | 87.5% | all |
| 146 | LRU Cache | Medium | Design | Data Structure Design | 47.4% | 87.5% | all |
| 3186 | Maximum Total Damage With Spell Casting | Medium | Arrays | Sorting / Prefix / Scan | 45.1% | 87.5% | all |
| 2361 | Minimum Costs Using the Train Line | Hard | Arrays | Sorting / Prefix / Scan | 77.9% | 87.5% | all |
| 1515 | Best Position for a Service Centre | Hard | Core DSA | Implementation / Reasoning | 35.3% | 87.5% | all |
| 2661 | First Completely Painted Row or Column | Medium | Core DSA | Implementation / Reasoning | 63.9% | 87.5% | all |
| 2702 | Minimum Operations to Make Numbers Non-positive | Hard | Arrays | Sorting / Prefix / Scan | 44.1% | 87.5% | all |
| 718 | Maximum Length of Repeated Subarray | Medium | Arrays | Sorting / Prefix / Scan | 51.4% | 87.5% | all |
| 56 | Merge Intervals | Medium | Arrays | Sorting / Prefix / Scan | 51.8% | 87.5% | all |
| 155 | Min Stack | Medium | Stack / Queue | Monotonic Stack / Simulation | 58.2% | 75.0% | 6m |
| 150 | Evaluate Reverse Polish Notation | Medium | Core DSA | Implementation / Reasoning | 57.8% | 75.0% | 6m |
| 1244 | Design A Leaderboard | Medium | Design | Data Structure Design | 68.1% | 75.0% | 6m |
| 3484 | Design Spreadsheet | Medium | Design | Data Structure Design | 74.1% | 75.0% | 6m |
| 287 | Find the Duplicate Number | Medium | Arrays | Sorting / Prefix / Scan | 64.3% | 75.0% | all |
| 380 | Insert Delete GetRandom O(1) | Medium | Core DSA | Implementation / Reasoning | 55.4% | 75.0% | all |
| 399 | Evaluate Division | Medium | Core DSA | Implementation / Reasoning | 64.2% | 75.0% | all |
| 460 | LFU Cache | Hard | Design | Data Structure Design | 49.2% | 75.0% | all |
| 2958 | Length of Longest Subarray With at Most K Frequency | Medium | Arrays | Sorting / Prefix / Scan | 56.6% | 75.0% | all |
| 759 | Employee Free Time | Hard | Core DSA | Implementation / Reasoning | 72.9% | 75.0% | all |
| 1229 | Meeting Scheduler | Medium | Greedy | Greedy | 55.2% | 75.0% | all |
| 23 | Merge k Sorted Lists | Hard | Arrays; Linked List; Heap | Sorting / Prefix / Scan; Two Pointers; Priority Queue | 59.6% | 62.5% | all |
| 124 | Binary Tree Maximum Path Sum | Hard | Arrays; Trees | Sorting / Prefix / Scan; DFS / BFS | 42.3% | 62.5% | all |
| 200 | Number of Islands | Medium | Graphs | BFS / DFS / Topological Sort | 64.4% | 62.5% | all |
| 297 | Serialize and Deserialize Binary Tree | Hard | Trees; Design | DFS / BFS; Data Structure Design | 60.8% | 62.5% | all |
| 49 | Group Anagrams | Medium | Strings | Hashing / Sliding Window | 72.6% | 62.5% | all |
| 622 | Design Circular Queue | Medium | Stack / Queue; Design | Monotonic Stack / Simulation; Data Structure Design | 54.7% | 62.5% | all |
| 412 | Fizz Buzz | Easy | Core DSA | Implementation / Reasoning | 75.5% | 62.5% | all |
| 765 | Couples Holding Hands | Hard | Core DSA | Implementation / Reasoning | 59.4% | 62.5% | all |
| 210 | Course Schedule II | Medium | Graphs | BFS / DFS / Topological Sort | 55.5% | 62.5% | all |
| 69 | Sqrt(x) | Easy | Binary Search | Binary Search | 41.8% | 62.5% | all |
| 1606 | Find Servers That Handled Most Number of Requests | Hard | Core DSA | Implementation / Reasoning | 45.4% | 62.5% | all |
| 332 | Reconstruct Itinerary | Hard | Core DSA | Implementation / Reasoning | 44.6% | 62.5% | all |
| 1004 | Max Consecutive Ones III | Medium | Core DSA | Implementation / Reasoning | 67.7% | 62.5% | all |
| 2598 | Smallest Missing Non-negative Integer After Operations | Medium | Arrays | Sorting / Prefix / Scan | 56.0% | 62.5% | all |
| 37 | Sudoku Solver | Hard | Backtracking | Backtracking | 65.5% | 50.0% | all |
| 39 | Combination Sum | Medium | Arrays; Backtracking | Sorting / Prefix / Scan; Backtracking | 76.5% | 50.0% | all |
| 46 | Permutations | Medium | Backtracking | Backtracking | 81.9% | 50.0% | all |
| 1048 | Longest String Chain | Medium | Strings | Hashing / Sliding Window | 63.0% | 50.0% | all |
| 123 | Best Time to Buy and Sell Stock III | Hard | Core DSA | Implementation / Reasoning | 53.7% | 50.0% | all |
| 207 | Course Schedule | Medium | Graphs | BFS / DFS / Topological Sort | 51.4% | 50.0% | all |
| 221 | Maximal Square | Medium | Core DSA | Implementation / Reasoning | 50.3% | 50.0% | all |
| 279 | Perfect Squares | Medium | Core DSA | Implementation / Reasoning | 56.5% | 50.0% | all |
| 1268 | Search Suggestions System | Medium | Binary Search | Binary Search | 65.2% | 50.0% | all |
| 642 | Design Search Autocomplete System | Hard | Binary Search; Design | Binary Search; Data Structure Design | 50.0% | 50.0% | all |
| 79 | Word Search | Medium | Strings; Binary Search | Hashing / Sliding Window; Binary Search | 47.4% | 50.0% | all |
| 208 | Implement Trie (Prefix Tree) | Medium | Trees | DFS / BFS | 69.5% | 50.0% | all |
| 631 | Design Excel Sum Formula | Hard | Arrays; Design | Sorting / Prefix / Scan; Data Structure Design | 39.7% | 50.0% | all |
| 1670 | Design Front Middle Back Queue | Medium | Stack / Queue; Design | Monotonic Stack / Simulation; Data Structure Design | 57.9% | 50.0% | all |
| 767 | Reorganize String | Medium | Strings | Hashing / Sliding Window | 57.1% | 50.0% | all |
| 1203 | Sort Items by Groups Respecting Dependencies | Hard | Arrays | Sorting / Prefix / Scan | 65.9% | 50.0% | all |
| 346 | Moving Average from Data Stream | Easy | Core DSA | Implementation / Reasoning | 80.2% | 50.0% | all |
| 2044 | Count Number of Maximum Bitwise-OR Subsets | Medium | Arrays; Backtracking | Sorting / Prefix / Scan; Backtracking | 89.5% | 50.0% | all |
| 126 | Word Ladder II | Hard | Strings | Hashing / Sliding Window | 27.7% | 50.0% | all |
| 17 | Letter Combinations of a Phone Number | Medium | Strings; Backtracking | Hashing / Sliding Window; Backtracking | 66.1% | 50.0% | all |
| 70 | Climbing Stairs | Easy | Dynamic Programming | State Transition | 54.1% | 50.0% | all |
| 256 | Paint House | Medium | Core DSA | Implementation / Reasoning | 64.4% | 50.0% | all |
| 1632 | Rank Transform of a Matrix | Hard | Arrays | Sorting / Prefix / Scan | 42.2% | 50.0% | all |
| 300 | Longest Increasing Subsequence | Medium | Dynamic Programming | State Transition | 59.4% | 50.0% | all |
| 103 | Binary Tree Zigzag Level Order Traversal | Medium | Trees | DFS / BFS | 63.7% | 50.0% | all |
| 50 | Pow(x, n) | Medium | Core DSA | Implementation / Reasoning | 38.7% | 50.0% | all |
| 875 | Koko Eating Bananas | Medium | Binary Search | Binary Search | 50.0% | 50.0% | all |
| 149 | Max Points on a Line | Hard | Core DSA | Implementation / Reasoning | 30.7% | 50.0% | all |
| 5 | Longest Palindromic Substring | Medium | Strings; Trees | Hashing / Sliding Window; DFS / BFS | 37.8% | 50.0% | all |
| 1010 | Pairs of Songs With Total Durations Divisible by 60 | Medium | Core DSA | Implementation / Reasoning | 53.5% | 50.0% | all |
| 204 | Count Primes | Medium | Core DSA | Implementation / Reasoning | 36.1% | 50.0% | all |
| 253 | Meeting Rooms II | Medium | Greedy | Greedy | 52.7% | 50.0% | all |
| 34 | Find First and Last Position of Element in Sorted Array | Medium | Arrays | Sorting / Prefix / Scan | 48.9% | 50.0% | all |
| 31 | Next Permutation | Medium | Backtracking | Backtracking | 45.3% | 50.0% | all |
| 98 | Validate Binary Search Tree | Medium | Strings; Trees; Binary Search | Hashing / Sliding Window; DFS / BFS; Binary Search | 35.8% | 50.0% | all |
| 343 | Integer Break | Medium | Core DSA | Implementation / Reasoning | 62.3% | 50.0% | all |
| 151 | Reverse Words in a String | Medium | Strings | Hashing / Sliding Window | 56.4% | 50.0% | all |
| 1155 | Number of Dice Rolls With Target Sum | Medium | Arrays | Sorting / Prefix / Scan | 62.3% | 50.0% | all |
| 465 | Optimal Account Balancing | Hard | Core DSA | Implementation / Reasoning | 50.5% | 50.0% | all |
| 188 | Best Time to Buy and Sell Stock IV | Hard | Core DSA | Implementation / Reasoning | 50.1% | 50.0% | all |
| 53 | Maximum Subarray | Medium | Arrays | Sorting / Prefix / Scan | 53.3% | 50.0% | all |
| 1 | Two Sum | Easy | Arrays | Sorting / Prefix / Scan; Two Pointers | 57.5% | 50.0% | all |
| 782 | Transform to Chessboard | Hard | Core DSA | Implementation / Reasoning | 51.3% | 50.0% | all |
| 981 | Time Based Key-Value Store | Medium | Core DSA | Implementation / Reasoning | 49.9% | 50.0% | all |
| 588 | Design In-Memory File System | Hard | Design | Data Structure Design | 48.4% | 50.0% | all |
| 714 | Best Time to Buy and Sell Stock with Transaction Fee | Medium | Core DSA | Implementation / Reasoning | 72.0% | 50.0% | all |
| 688 | Knight Probability in Chessboard | Medium | Core DSA | Implementation / Reasoning | 57.0% | 50.0% | all |