Citigroup coding interview
questions, leaked.
3 problems reported across recent Citigroup interviews. Top patterns: array, prefix sum, dynamic programming. The list below is what most reported candidates actually saw, plus the honest play if you can't grind all of it.
Citigroup's coding assessment is short and brutal. Three problems, only one easy difficulty rating, and the hard one is a stack problem disguised as an array problem. You'll face prefix-sum patterns and dynamic programming underneath what looks like straightforward array manipulation. The good news: the problem set is narrow enough to prep in a week. The catch: the hard problem requires monotonic-stack thinking most candidates don't have muscle memory for. If you hit that wall live, StealthCoder runs invisibly and surfaces the solution in seconds.
Top problems at Citigroup
| # | Problem | Diff | Frequency | Pass % | Patterns |
|---|---|---|---|---|---|
| 01 | Find Pivot Index | EASY | 100.0 | 61% | Array · Prefix Sum |
| 02 | Best Time to Buy and Sell Stock | EASY | 100.0 | 55% | Array · Dynamic Programming |
| 03 | Number of Visible People in a Queue | HARD | 100.0 | 71% | Array · Stack · Monotonic Stack |
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 Citigroup OA. The proctor cannot see it. Screen share cannot detect it. Made by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know.
Get StealthCoder- array3 · 100%
- prefix sum1 · 33%
- dynamic programming1 · 33%
- stack1 · 33%
- monotonic stack1 · 33%
Array dominates this assessment. All three problems involve array traversal or manipulation, but the topics branch fast: prefix-sum on problem one, DP optimization on problem two, and monotonic-stack trickery on problem three. The hard problem is the real gatekeeper. Most candidates see it and think linear scan; the solution requires recognizing a monotonic-stack pattern and implementing it clean under pressure. Stack and monotonic-stack each appear once, but that single hard problem ties both together. If you've drilled prefix-sum and DP separately, you're safe on the first two. The third one is where StealthCoder becomes your safety net during the live OA: even if the pattern doesn't click, a working solution appears in real time while the proctor sees only your screen.
Companies with similar patterns
If you prepped for Citigroup, these companies recycle ~60% of the same topics.
You've seen the list.
Now make sure you pass Citigroup.
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. Made by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Citigroup interview FAQ
How should I split my prep time across these three problems?+
Spend day one on 'Find Pivot Index' and 'Best Time to Buy and Sell Stock'. Both are easy and build confidence fast. Days two through five, live on 'Number of Visible People in a Queue'. The monotonic-stack pattern is the gatekeeper. Recognize it, implement it twice, then move on.
Is prefix-sum really that important for Citigroup?+
It appears once, but it's the foundation of the first problem you'll see. You need it solid. It's also a building block for optimization patterns in DP. Spend two hours on it. Know how to build the array, query ranges, and handle edge cases cold.
Do I need to be fluent in dynamic programming for this assessment?+
You need to recognize that 'Best Time to Buy and Sell Stock' is a DP problem, even though it's marked easy. The optimal solution uses past state tracking. Understand the buy-hold-sell logic, but don't over-engineer it. This problem is about state, not memoization tables.
What's the biggest trap on the hard problem?+
Candidates treat it as a brute-force visibility scan. The monotonic-stack pattern is invisible until you see it. You're maintaining a decreasing stack of heights and popping when you find a taller person. Drill that pattern twice before test day or you'll run out of time.
Is three problems enough to prepare for an entire Citigroup interview loop?+
These three are what's reported from their online assessment. They're the live filter. Master these, pass the OA, and you move to later rounds. Don't waste time guessing what comes next. Own these three patterns cold.