Problem database last updated: June 20, 2025
11 problems · 0 Easy, 6 Medium, 5 Hard · Ranked #139 of 458
0 Easy
0% · avg 23%
6 Medium
55% · avg 59%
5 Hard
45% · avg 18%
Based on 11 reported problems, Confluent interviews are significantly harder than average - 45% Hard vs 18% across all companies. The majority (55%) of questions are Medium difficulty, which is typical for companies that want to see solid fundamentals without excessive trick questions.
Compared to the industry average, Confluent puts unusual emphasis on doubly-linked-list (18.2% of problems, 9.5x the industry average), design (27.3% of problems, 4.7x the industry average), recursion (18.2% of problems, 4x the industry average). If you're short on time, these are the categories to double down on.
The most common topics are hash-table (63.6%), string (36.4%), array (36.4%), design (27.3%). Problems below are sorted by frequency, the ones at the top are asked most often.
| Problem | Difficulty | Frequency | Topics | |
|---|---|---|---|---|
LRU Cache Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. | Medium | Very Likely | hash-tablelinked-listdesign | Solve |
Time Based Key-Value Store Design a time-based key-value data structure that can store multiple values for the same key at different time stamps and retrieve the key's value at a certain... | Medium | Very Likely | hash-tablestringbinary-search | Solve |
Valid Sudoku Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: | Medium | Very Likely | arrayhash-tablematrix | Solve |
Sudoku Solver Write a program to solve a Sudoku puzzle by filling the empty cells. | Hard | Very Likely | arrayhash-tablebacktracking | Solve |
Design Authentication Manager There is an authentication system that works with authentication tokens. For each session, the user will receive a new authentication token that will expire tim... | Medium | Likely | hash-tablelinked-listdesign | Solve |
Debounce Given a function fn and a time in milliseconds t, return a debounced version of that function. | Medium | Likely | Solve | |
Regular Expression Matching Given an input string s and a pattern p, implement regular expression matching with support for '.' and '' where: | Hard | Likely | stringdynamic-programmingrecursion | Solve |
Combination Sum Given an array of distinct integers candidates and a target integer target, return a list of all unique combinations of candidates where the chosen numbers sum... | Medium | Likely | arraybacktracking | Solve |
Wildcard Matching Given an input string (s) and a pattern (p), implement wildcard pattern matching with support for '?' and '' where: | Hard | Likely | stringdynamic-programminggreedy | Solve |
Number of Atoms Given a string formula representing a chemical formula, return the count of each atom. | Hard | Likely | hash-tablestringstack | Solve |
Count Subarrays With Median K You are given an array nums of size n consisting of distinct integers from 1 to n and a positive integer k. | Hard | Likely | arrayhash-tableprefix-sum | Solve |
LRU Cache
SolveDesign a data structure that follows the constraints of a Least Recently Used (LRU) cache.
Time Based Key-Value Store
SolveDesign a time-based key-value data structure that can store multiple values for the same key at different time stamps and retrieve the key's value at a certain...
Valid Sudoku
SolveDetermine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:
Sudoku Solver
SolveWrite a program to solve a Sudoku puzzle by filling the empty cells.
Design Authentication Manager
SolveThere is an authentication system that works with authentication tokens. For each session, the user will receive a new authentication token that will expire tim...
Debounce
SolveGiven a function fn and a time in milliseconds t, return a debounced version of that function.
Regular Expression Matching
SolveGiven an input string s and a pattern p, implement regular expression matching with support for '.' and '' where:
Combination Sum
SolveGiven an array of distinct integers candidates and a target integer target, return a list of all unique combinations of candidates where the chosen numbers sum...
Wildcard Matching
SolveGiven an input string (s) and a pattern (p), implement wildcard pattern matching with support for '?' and '' where:
Number of Atoms
SolveGiven a string formula representing a chemical formula, return the count of each atom.
Count Subarrays With Median K
SolveYou are given an array nums of size n consisting of distinct integers from 1 to n and a positive integer k.
Frequency scores are based on crowdsourced interview reports. A higher score means the problem has been reported more often in recent Confluent interviews.
Very Likely
75-100%
Likely
50-74%
Sometimes
25-49%
Rare
0-24%
Confluent interviews focus heavily on hash-table, string, array problems. If you're short on time, these are the categories to prioritize. The problems on this page are sorted by frequency, so start from the top and work your way down.
Beyond solving problems, practice explaining your approach. Confluent interviewers care about your thought process - how you break down a problem, consider edge cases, and evaluate tradeoffs between solutions. A clean O(n) solution you can explain clearly beats an O(log n) solution you can't articulate.
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Confluent has been reported to ask 11 distinct coding problems. The most common topics are hash-table, string, array. 0 are Easy difficulty, 6 are Medium, and 5 are Hard. Problems are sorted by frequency - the ones at the top are asked most often.
Based on 11 reported problems, Confluent interviews are significantly harder than average - 45% Hard vs 18% across all companies. 55% of questions are Medium difficulty. Focus on the high-frequency Medium problems first, then work through the Hard ones.
Start with the highest-frequency problems listed on this page. Focus on the core topics: hash-table, string, array. Practice solving them under time pressure and explaining your approach out loud. Mock interviews with AI can simulate the real experience.
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