Citadel coding interview
questions, leaked.
101 problems reported across recent Citadel interviews. Top patterns: array, dynamic programming, string. The list below is what most candidates actually saw, plus the honest play if you can't grind all of it.
Citadel's coding assessment is front-loaded with arrays and dynamic programming. You're looking at 101 problems across their interview loop, with 60 medium-difficulty questions that form the real gauntlet. Arrays alone show up in 62 problems, and DP in 29. Most candidates freeze on problems like Longest Non-decreasing Subarray or Sliding Window Maximum mid-interview. If you hit a wall on the live assessment, StealthCoder runs invisibly and surfaces a working solution in seconds, invisible to the proctor. That's your safety net for whatever didn't make it into your final week of prep.
Top problems at Citadel
| # | Problem | Diff | Frequency | Pass % | Patterns |
|---|---|---|---|---|---|
| 01 | Longest Non-decreasing Subarray From Two Arrays | MEDIUM | 100.0 | 30% | Array · Dynamic Programming |
| 02 | Binary Tree Maximum Path Sum | HARD | 98.7 | 41% | Dynamic Programming · Tree · Depth-First Search |
| 03 | Minimum Knight Moves | MEDIUM | 93.4 | 41% | Breadth-First Search |
| 04 | Delete and Earn | MEDIUM | 93.4 | 57% | Array · Hash Table · Dynamic Programming |
| 05 | Palindromic Substrings | MEDIUM | 86.5 | 72% | Two Pointers · String · Dynamic Programming |
| 06 | Sliding Window Maximum | HARD | 85.3 | 48% | Array · Queue · Sliding Window |
| 07 | Count Palindromic Subsequences | HARD | 81.3 | 39% | String · Dynamic Programming |
| 08 | LFU Cache | HARD | 79.8 | 47% | Hash Table · Linked List · Design |
| 09 | Minimum Equal Sum of Two Arrays After Replacing Zeros | MEDIUM | 79.8 | 50% | Array · Greedy |
| 10 | Minimum Operations to Make Numbers Non-positive | HARD | 78.1 | 42% | Array · Binary Search |
| 11 | Number of Good Binary Strings | MEDIUM | 76.4 | 52% | Dynamic Programming |
| 12 | Maximum Total Damage With Spell Casting | MEDIUM | 76.4 | 28% | Array · Hash Table · Two Pointers |
| 13 | LRU Cache | MEDIUM | 74.4 | 45% | Hash Table · Linked List · Design |
| 14 | Best Position for a Service Centre | HARD | 74.4 | 35% | Array · Math · Geometry |
| 15 | Maximum Length of Repeated Subarray | MEDIUM | 74.4 | 51% | Array · Binary Search · Dynamic Programming |
| 16 | Minimum Costs Using the Train Line | HARD | 74.4 | 78% | Array · Dynamic Programming |
| 17 | Evaluate Division | MEDIUM | 72.3 | 63% | Array · String · Depth-First Search |
| 18 | First Completely Painted Row or Column | MEDIUM | 72.3 | 64% | Array · Hash Table · Matrix |
| 19 | Merge Intervals | MEDIUM | 70.0 | 49% | Array · Sorting |
| 20 | Longest String Chain | MEDIUM | 70.0 | 62% | Array · Hash Table · Two Pointers |
| 21 | Best Time to Buy and Sell Stock | EASY | 67.4 | 55% | Array · Dynamic Programming |
| 22 | Find the Duplicate Number | MEDIUM | 67.4 | 63% | Array · Two Pointers · Binary Search |
| 23 | Serialize and Deserialize Binary Tree | HARD | 67.4 | 59% | String · Tree · Depth-First Search |
| 24 | Insert Delete GetRandom O(1) | MEDIUM | 64.5 | 55% | Array · Hash Table · Math |
| 25 | Evaluate Reverse Polish Notation | MEDIUM | 64.5 | 55% | Array · Math · Stack |
| 26 | Parallel Courses III | HARD | 61.1 | 67% | Array · Dynamic Programming · Graph |
| 27 | Number of Islands | MEDIUM | 61.1 | 62% | Array · Depth-First Search · Breadth-First Search |
| 28 | Length of Longest Subarray With at Most K Frequency | MEDIUM | 61.1 | 56% | Array · Hash Table · Sliding Window |
| 29 | Sudoku Solver | HARD | 61.1 | 64% | Array · Hash Table · Backtracking |
| 30 | Meeting Scheduler | MEDIUM | 57.1 | 55% | Array · Two Pointers · Sorting |
| 31 | Employee Free Time | HARD | 57.1 | 73% | Array · Line Sweep · Sorting |
| 32 | Couples Holding Hands | HARD | 57.1 | 58% | Greedy · Depth-First Search · Breadth-First Search |
| 33 | Robot Room Cleaner | HARD | 57.1 | 78% | Backtracking · Interactive |
| 34 | Find Median from Data Stream | HARD | 57.1 | 53% | Two Pointers · Design · Sorting |
| 35 | Group Anagrams | MEDIUM | 57.1 | 71% | Array · Hash Table · String |
| 36 | Validate Binary Search Tree | MEDIUM | 57.1 | 34% | Tree · Depth-First Search · Binary Search Tree |
| 37 | Permutations | MEDIUM | 57.1 | 81% | Array · Backtracking |
| 38 | Merge k Sorted Lists | HARD | 57.1 | 57% | Linked List · Divide and Conquer · Heap (Priority Queue) |
| 39 | Binary Tree Zigzag Level Order Traversal | MEDIUM | 52.2 | 62% | Tree · Breadth-First Search · Binary Tree |
| 40 | Search Suggestions System | MEDIUM | 52.2 | 65% | Array · String · Binary Search |
| 41 | Trapping Rain Water | HARD | 52.2 | 65% | Array · Two Pointers · Dynamic Programming |
| 42 | N-Queens | HARD | 52.2 | 73% | Array · Backtracking |
| 43 | Design Search Autocomplete System | HARD | 52.2 | 49% | String · Depth-First Search · Design |
| 44 | Regular Expression Matching | HARD | 52.2 | 29% | String · Dynamic Programming · Recursion |
| 45 | Best Time to Buy and Sell Stock II | MEDIUM | 52.2 | 70% | Array · Dynamic Programming · Greedy |
| 46 | Design Circular Queue | MEDIUM | 52.2 | 53% | Array · Linked List · Design |
| 47 | Fizz Buzz | EASY | 52.2 | 74% | Math · String · Simulation |
| 48 | Combination Sum | MEDIUM | 52.2 | 75% | Array · Backtracking |
| 49 | Best Time to Buy and Sell Stock III | HARD | 52.2 | 51% | Array · Dynamic Programming |
| 50 | Find Servers That Handled Most Number of Requests | HARD | 45.9 | 44% | Array · Greedy · Heap (Priority Queue) |
Frequencies derived from public community-tagged interview reports. Click a row to view on LeetCode.
You have a week, maybe less. You can't out-grind the list above. StealthCoder runs invisibly during the actual Citadel OA. The proctor cannot see it. Screen share cannot detect it. Built by an engineer who got tired of watching his cohort grind for six months and still get filtered at the OA stage.
Get StealthCoder- array62 · 61%
- dynamic programming29 · 29%
- string22 · 22%
- hash table21 · 21%
- breadth first search19 · 19%
- depth first search16 · 16%
- math15 · 15%
- sorting13 · 13%
- design12 · 12%
- graph11 · 11%
The pattern is clear: Citadel rewards pattern recognition over raw speed. Array problems dominate, but they're almost always fused with DP, hash tables, or string manipulation. Sliding Window Maximum and Binary Tree Maximum Path Sum are signature hard problems that require both algorithm fluency and implementation discipline. The difficulty skew is brutal: 36 hard problems means you'll face at least one or two in your actual interview. Your prep should start with array fundamentals and DP recurrence relations, then move into the hybrid problems that combine strings with DP. Breadth-first search (19 problems) and depth-first search (16) appear frequently but secondary. Hash table design shows up in cache problems (LRU, LFU) that test systems thinking. If you blank on a design pattern or a two-pointer optimization mid-assessment, StealthCoder is your hedge.
Companies with similar patterns
If you prepped for Citadel, these companies recycle ~60% of the same topics.
You've seen the list.
Now make sure you pass Citadel.
Memorizing every problem above in a week is a fantasy. StealthCoder is the hedge: an AI overlay that's invisible during screen share. It reads the problem on screen and surfaces a working solution in under 2 seconds. Built by an engineer who got tired of watching his cohort grind for six months and still get filtered at the OA stage. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Citadel interview FAQ
Should I study array problems first for Citadel?+
Yes. Arrays appear in 62 of 101 problems and almost always pair with DP or hash tables. Master sliding windows, two pointers, and prefix sums first. Then layer in DP recurrence. Problems like Longest Non-decreasing Subarray combine both, so drilling arrays early unlocks the harder fusion problems.
How many dynamic programming problems should I solve?+
Citadel has 29 DP problems spread across their interview set. You won't see them in isolation. Solve at least 15 to 20 classical DP problems (knapsack, longest subsequence, counting paths), then focus on hybrid DP plus array or string problems that appear in their actual list.
Are string problems important for Citadel?+
Moderately. String appears in 22 problems, usually paired with DP or two pointers. Palindromic Substrings and Count Palindromic Subsequences are representative. If you're weak on string DP, these two patterns will appear. Don't neglect them, but prioritize array and core DP first.
What should I do if I see a design problem like LFU Cache?+
Design shows up in 12 problems, mostly hash table plus linked list implementations. LFU and LRU Cache are classic. These require systems thinking and data structure stacking. Practice building caches with custom eviction logic. Expect one design problem in the real interview.
How much time should I spend on graph and tree problems?+
Less than array and DP, but not zero. Breadth-first search (19 problems) and depth-first search (16) matter, especially for tree traversal and shortest-path problems. Binary Tree Maximum Path Sum is a signature hard problem. Drill 8 to 10 tree and graph problems, then pivot back to array hybrids.