Problem database last updated: June 20, 2025
4 problems · 0 Easy, 3 Medium, 1 Hard · Ranked #305 of 458
0 Easy
0% · avg 23%
3 Medium
75% · avg 59%
1 Hard
25% · avg 18%
Based on 4 reported problems, Duolingo interviews are slightly harder than average - 25% Hard vs 18% across all companies. The majority (75%) 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, Duolingo puts unusual emphasis on hash-table (75% of problems, 3.3x the industry average), array (100% of problems, 1.7x the industry average). If you're short on time, these are the categories to double down on.
The most common topics are array (100%), hash-table (75%), string (25%), design (25%). Problems below are sorted by frequency, the ones at the top are asked most often.
| Problem | Difficulty | Frequency | Topics | |
|---|---|---|---|---|
Encrypt and Decrypt Strings You are given a character array keys containing unique characters and a string array values containing strings of length 2. You are also given another string ar... | Hard | Very Likely | arrayhash-tablestring | Solve |
Minimum Number of People to Teach On a social network consisting of m users and some friendships between users, two users can communicate with each other if they know a common language. | Medium | Very Likely | arrayhash-tablegreedy | Solve |
K Radius Subarray Averages You are given a 0-indexed array nums of n integers, and an integer k. | Medium | Very Likely | arraysliding-window | Solve |
Task Scheduler II You are given a 0-indexed array of positive integers tasks, representing tasks that need to be completed in order, where tasks[i] represents the type of the ith... | Medium | Likely | arrayhash-tablesimulation | Solve |
Encrypt and Decrypt Strings
SolveYou are given a character array keys containing unique characters and a string array values containing strings of length 2. You are also given another string ar...
Minimum Number of People to Teach
SolveOn a social network consisting of m users and some friendships between users, two users can communicate with each other if they know a common language.
K Radius Subarray Averages
SolveYou are given a 0-indexed array nums of n integers, and an integer k.
Task Scheduler II
SolveYou are given a 0-indexed array of positive integers tasks, representing tasks that need to be completed in order, where tasks[i] represents the type of the ith...
Frequency scores are based on crowdsourced interview reports. A higher score means the problem has been reported more often in recent Duolingo interviews.
Very Likely
75-100%
Likely
50-74%
Sometimes
25-49%
Rare
0-24%
Duolingo interviews focus heavily on array, hash-table, string 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. Duolingo 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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Duolingo has been reported to ask 4 distinct coding problems. The most common topics are array, hash-table, string. 0 are Easy difficulty, 3 are Medium, and 1 are Hard. Problems are sorted by frequency - the ones at the top are asked most often.
Based on 4 reported problems, Duolingo interviews are slightly harder than average - 25% Hard vs 18% across all companies. 75% 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: array, hash-table, string. 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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