30 LeetCode Interview Questions for 2026

Practice 30 LeetCode interview questions grouped by pattern, with timing, fresher vs. experienced advice, and the skills interviewers actually test.

LeetCode questions: 30 most asked interview questions (2026)

Candidates grind hundreds of LeetCode problems and still freeze the moment an interviewer changes a constraint. The problem isn't effort. It's approach. Most prep plans optimize for volume — solve more, solve faster, solve again. But interviewers don't score you on whether you've seen the exact problem before. They score you on whether you can reason through a new one.

This guide takes a different angle. Thirty problems, grouped by technique, chosen because they show up repeatedly in real technical interviews. Not because memorizing them will save you — but because the patterns behind them will.

Why pattern recognition beats memorization

One engineer solved over 200 problems in six months, then froze when an interviewer changed a single constraint on a problem they'd already solved. The memorized solution didn't transfer. The pattern they hadn't internalized couldn't help them adapt.

That story is common. Experienced interviewers say the same thing: they want candidates who write solid, maintainable code and ask good questions when requirements are vague. They're not checking whether you've seen the problem. They're checking whether you can think.

LeetCode knowledge alone usually isn't enough. The questions are a vehicle for demonstrating reasoning, communication, and adaptability — not an end in themselves. That's the lens to bring to every problem on this list.

How to use this list

This isn't a full prep curriculum. It's a focused set of problems that cover the patterns interviewers test most. How you approach them depends on where you are.

• Freshers: Start with Easy problems to build pattern fluency. Target 10–20 problems per topic before moving to Medium. The goal is recognition speed, not memorization.
• Experienced candidates: Go straight to Medium and Hard. Focus on complexity trade-offs, edge cases, and follow-up variants — that's where interviewers probe depth.
• Everyone: Use 25–30 minute timed sessions per problem. Spend the first 5 minutes understanding the problem, 20 minutes solving, and 10 minutes studying the solution afterward. Don't go past 30–35 minutes total. If you're stuck, study the solution and revisit the problem in a week.

The 30 most asked LeetCode interview questions

Problems are grouped by technique, not difficulty. Interviewers test pattern transfer — whether you can apply a technique you've practiced to a problem you haven't seen. That's why the grouping matters more than the number.

Arrays and two pointers

• Two Sum — the canonical warm-up; tests hash map intuition and whether you default to brute force
• Rotate Array — in-place manipulation; interviewers watch for off-by-one errors and space awareness
• Best Time to Buy and Sell Stock — single-pass greedy; a common phone screen opener
• Container With Most Water — two-pointer convergence; tests whether you can articulate why the pointer moves
• 3Sum — sorting + two pointers; follow-ups on deduplication are standard

Interviewers use array problems to gauge how quickly you reach for the right data structure instead of nested loops.

Sliding window

• Longest Substring Without Repeating Characters — the classic variable-window problem
• Longest Repeating Character Replacement — fixed-window variant; tests whether you understand the window invariant
• Minimum Window Substring — harder; interviewers expect you to explain contraction logic clearly
• Maximum Average Subarray I — straightforward fixed-window; good for building the pattern before harder variants

The sliding window signal in interviews: can you maintain and reason about a window invariant under pressure?

Linked lists

• Reverse Linked List — if you can't do this in your sleep, start here
• Merge Two Sorted Lists — recursive vs. iterative; interviewers often ask for both
• Linked List Cycle — slow/fast pointer detection; follow-up: find the cycle start
• Remove Nth Node From End of List — two-pointer gap technique

The slow/fast pointer pattern appears in linked list problems and beyond. Learn it once, apply it everywhere.

Trees and BFS/DFS

• Binary Tree Level Order Traversal — BFS baseline; interviewers use it to test queue mechanics
• Validate Binary Search Tree — in-order traversal or range-based recursion; a common follow-up trap
• Number of Islands — grid DFS; one of the most frequently asked graph problems across all companies
• Course Schedule — topological sort via DFS; tests cycle detection in directed graphs
• Maximum Depth of Binary Tree — simple recursion; often a warm-up before harder tree problems

BFS vs. DFS is a common follow-up question. Know when each is appropriate and be ready to explain why.

Dynamic programming

• Climbing Stairs — the entry point to DP; if you can explain the recurrence, you understand the concept
• Coin Change — unbounded knapsack variant; interviewers probe whether you can optimize from top-down to bottom-up
• Longest Increasing Subsequence — O(n²) vs. O(n log n); experienced candidates are expected to discuss both
• House Robber — linear DP with a clear real-world analogy; good for practicing explanation

DP problems are where experienced candidates are expected to discuss optimization trade-offs, not just produce a working solution.

Stacks, queues, and design

• Valid Parentheses — stack fundamentals; often the first question in a phone screen
• Min Stack — design under constraints; tests whether you think about auxiliary data structures
• Implement Queue Using Stacks — amortized analysis; interviewers care about your explanation of amortized O(1)
• LRU Cache — hash map + doubly linked list; a design problem that tests implementation precision

Design problems test communication as much as code. Walk through your data structure choices before writing anything.

Binary search

• First Bad Version — binary search on answer-space; the simplest version of a powerful pattern
• Search in Rotated Sorted Array — modified binary search; interviewers watch for how you handle the pivot
• Find Minimum in Rotated Sorted Array — variant that tests the same intuition from a different angle

Binary search on answer-space is a common follow-up variant. If you only know binary search on sorted arrays, you're missing half the pattern.

Hash tables and prefix sums

• First Unique Character in a String — frequency counting baseline
• Subarray Sum Equals K — prefix sum + hash map; a pattern that appears in many medium-difficulty problems

Frequency counting and prefix sums look similar on the surface but solve different classes of problems. Worth keeping them distinct in your head.

Fresher vs. experienced: what interviewers actually expect

If you're a fresher

Focus on Easy and lower Medium problems. Show pattern recognition and clean code — not cleverness. Target 40 or more problems across core topics before your first real interview. That's roughly the minimum to build reliable pattern fluency.

Interviewers expect you to think aloud and ask clarifying questions. Producing a perfect solution silently is not what they're evaluating. They want to see how you break down a problem, identify constraints, and communicate your approach.

If you're experienced

Medium and Hard problems. Interviewers probe complexity analysis, edge cases, and follow-up variants. They expect you to discuss trade-offs — why this approach over that one, what breaks at scale, what changes if the input is streamed.

Some companies have also shifted toward asking candidates to build small applications instead of only solving algorithmic puzzles. If you're interviewing at startups or companies with practical engineering cultures, be ready for that format too.

How to practice LeetCode for interviews without burning out

Volume without structure leads to burnout. Structure without pressure leads to false confidence. Here's what actually works:

• Timed sessions. Practice in 30–45 minute sprints to mimic real interview pressure. If you're solving problems in a relaxed, untimed environment, you're training a skill you won't have access to on the day.
• Track progress. Use a spreadsheet or a simple list. Mark problems as solved, partially solved, or needs-revisit. Come back to the needs-revisit pile weekly.
• Explain aloud. Narrate your reasoning as you solve. This is what interviewers evaluate — your thinking process, not your typing speed. If you can't explain your approach clearly while coding, you're not ready.
• Mix resources. LeetCode alone isn't enough. Pair it with a structured course for pattern theory, and mock interviews for pressure simulation. The combination builds both knowledge and performance under stress.
• Don't cram solutions. Pattern transfer, not recall, is what gets you hired. If you can't solve a variant of a problem you've already done, you memorized the answer instead of learning the technique.

A reasonable milestone: 60–70 medium problems is a solid point to feel ready for mock contests and real interviews. Getting there with purpose matters more than getting there fast.

Practice your LeetCode skills in a real interview setting

Solving problems alone doesn't replicate interview pressure. It's one thing to work through a problem in your IDE with no one watching, and another to do it while someone is evaluating your every word.

Verve AI's mock interviews simulate that pressure. You practice explaining solutions under real conditions, handle follow-up questions the way an interviewer would ask them, and get structured feedback on your communication — not just whether your code passes. The AI Interview Copilot also works during live interviews, listening in real time and suggesting approaches when you need them most.

You can try it free — three sessions, no credit card. Enough to see whether practicing under pressure changes how you perform.

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Thirty problems. Eight patterns. The list is short on purpose. Interviewers don't test how many problems you've solved. They test whether you can reason through the one they put in front of you. Practice with purpose, explain your thinking, and the patterns will do the rest.