Citadel backend engineer interviews typically focus on APIs, databases, system design, concurrency, caching, and data structures.
1. DAG Order Validator
Category: Topological sort coding problem
DAG Order Validator Given a Directed Acyclic Graph (DAG) and a list of nodes, determine if the list represents a valid topological sort...
Input: Graph (nodes and edges)Output: Computed result
2. Expression Evaluator
Category: String coding problem
Expression Evaluator You need to design and implement an expression evaluator that parses and computes mathematical expressions formatted in...
Input: StringOutput: Computed result
3. Knight Moves on Phone
Category: String coding problem
Knight Moves on Phone This problem is split into two parts.
Input: ListOutput: Integer
4. Price Change Aggregator
Category: Algorithm coding problem
Price Change Aggregator You are building a system to aggregate price updates from multiple feeds to reconstruct the price history of an asset.
Input: ListOutput: Computed result
5. Visit All Cities
Category: Graph coding problem
Visit All Cities You are given a list of airline tickets where each ticket represents a directed edge from a departure airport to an arrival...
Input: Graph (nodes and edges)Output: Computed result
6. Social Network Friend Suggester
Category: Array coding problemBuild a friend recommendation system for a social network. Given
n users (indexed 0 to n - 1) and a list of existing friendships (undirected...Input: ArrayOutput: Array
7. Minimum Sum Tree Path
Category: Binary tree coding problem
Minimum Sum Tree Path
Input: Binary treeOutput: Computed result
8. Dial Pad Knight Paths
Category: Algorithm coding problem
Dial Pad Knight Paths
Input: Number(s)Output: Integer
9. Subsequence Goodness Values
Category: Array coding problem
Subsequence Goodness Values
Input: ArrayOutput: Integer
10. Sliding Window Top K
Category: Sliding window coding problem
Sliding Window Top K
Input: Array of integersOutput: Computed result
11. Price Stream Merger
Category: Heap-based coding problem
Price Stream Merger
Input: ListOutput: Computed result
12. Pandigital Addition Count
Category: Algorithm coding problem
Pandigital Addition Count
Input: Integer(s)Output: Computed result
13. Closest Point Pair
Category: Algorithm coding problem
Closest Point Pair
Input: ListOutput: Integer
14. Flight Itinerary Planner
Category: Graph coding problem
Flight Itinerary Planner
Input: Graph (nodes and edges)Output: Computed result
15. Process Schedule Counter
Category: Algorithm coding problem
Process Schedule Counter
Input: ListOutput: Integer
16. [CodeSignal] Common Free Slot
Category: Interval-based coding problem
[CodeSignal] Common Free Slot
Input: ListOutput: Computed result
17. [CodeSignal] Stable Server Segments
Category: Array coding problem
[CodeSignal] Stable Server Segments
Input: ArrayOutput: Computed result
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