Duolingo Coding Interview Questions
25 Duolingo coding interview problems with full optimal solutions — 17 easy, 6 medium, 2 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an Duolingo interviewer values, and a FAQ section.
Showing 2 problems of 25
- #212hardfoundational
212. Word Search II
Find all words from a dictionary that exist as paths in a letter grid — the trie-pruned DFS that Duolingo's word-puzzle feature uses to validate which target vocabulary words a learner can trace through a randomly generated tile board in one traversal.
- #295hardfoundational
295. Find Median from Data Stream
Maintain a running median as integers arrive one at a time using two heaps — the same dual-priority-queue structure Duolingo's spaced-repetition scheduler uses to track the median session-difficulty score across an evolving stream of lesson completions.