Arrays & Hashing in Data Structures & AlgorithmsInterview Readiness Check
Frequency maps, duplicate detection, anagram grouping — the foundation pattern that unlocks O(n) solutions.
Learning path
Try a sample question
Swiggy's analytics team needs to find the first duplicate restaurant ID in a list of 10M IDs streamed in order. What data structure gives O(1) average lookup to detect the first duplicate?
Sign up free to take the full check and see the answer with an explanation.
What this module tests
- Conceptual understanding of arrays & hashing fundamentals
- Trade-offs and design decisions in real system scenarios
- hashmap and frequency — applied knowledge
- Interview-style reasoning and explanation quality
Free to start
Take the Arrays & Hashing check →
10 questions · Dimension scoring · AI coach feedback · Shareable result
Test your knowledge — free →No credit card · Takes 10–15 min
Frequently asked questions
- What does the Arrays & Hashing check test?
- The check covers frequency maps, duplicate detection, anagram grouping — the foundation pattern that unlocks o(n) solutions. Questions span beginner to advanced difficulty and test both conceptual understanding and practical trade-off reasoning.
- What keywords should I know for Arrays & Hashing?
- Key concepts include: hashmap, frequency, duplicates, anagram, two-sum, prefix sum, O(n). These frequently appear in data structures & algorithms interviews at product and infrastructure companies.
- How many questions are in the check?
- Each check has 10 questions — a mix of MCQ and short-answer. You get scored by dimension (e.g., scalability, consistency) so you know exactly where to focus.
- How long does it take to study Arrays & Hashing?
- Most engineers spend around 2 hours on this module. The check itself takes about 10–15 minutes. You can retake it up to 3 times per day.
- What prerequisite knowledge do I need before Arrays & Hashing?
- Arrays & Hashing is a foundational module — no prerequisites needed.
- Is hashmap, frequency, duplicates covered?
- Yes. The Arrays & Hashing module covers hashmap, frequency, duplicates among other key concepts. The check includes questions that reflect real data structures & algorithms interview patterns.
What this unlocks
Two Pointers
Eliminate the inner loop — sort and converge from both ends …
Stack & Monotonic Stack
When previous elements affect current decisions — brackets, …
Binary Search
Search space reduction — not just sorted arrays but any prob…
Greedy Algorithms
Local optimal choices that produce global optimal — interval…
Bit Manipulation
XOR tricks, bitmasks, counting bits — power of 2, single num…