What the rounds are like
| Stage | What people usually describe |
|---|---|
| Phone or video screen | Resume talk, then one problem (sometimes two), about 60 minutes |
| Onsite coding | Up to 90 minutes, usually two problems |
Screen problems are often "build a small class" style rather than pure algorithms. One recent candidate also had the interviewer add rules as they went, like not using loops, so listen carefully and ask what's allowed.
What people have been asked
These come up in candidates' own write-ups of their interviews. We wrote the example prompts ourselves, so the wording you get will be different.
Plan a road trip between gas stations
A screening-round favorite: get a car across a grid to its destination without running out of gas. Follow-ups add gas stations and obstacles.
Work out which stations you can reach from each other, then it becomes a graph search.
How it might be asked
A car has to drive from a start point to an end point on a grid, and can only drive a fixed distance on a full tank. Given a list of gas station locations, can it make the trip?
Key concepts to know
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Add, remove and pick at random
A lottery that can add a person, remove a person and pick a random winner, all in O(1).
A hash map alone can't pick randomly, and a list alone can't remove quickly. You need both.
How it might be asked
Build a lottery system with add(person), remove(person) and pickRandom(). Every operation should run in constant time on average.
Key concepts to know
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Add two numbers one place at a time
From one recent loop: add two integers digit by digit, using recursion, without loops or adding the whole numbers directly.
It's mostly about following unusual rules carefully and handling the carry.
How it might be asked
Add two integers by place value: ones, then tens, then hundreds. You can only add single place values together, and you can't use loops, so use recursion.
Key concepts to know
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Crush repeated letters
Keep removing runs of three or more of the same letter until none are left.
Removing one run can join two others into a new one. Rescanning is slow, so keep a stack of letters and counts.
How it might be asked
Given a string, remove any group of three or more of the same letter in a row, and keep doing it as new groups form. Return what's left.
Key concepts to know
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How to approach a problem
- Say it back and ask questions. How big is the input? What are the edge cases? What should you return?
- Start with brute force. Say it out loud with its complexity so you've got something to beat.
- Figure out what it really is. Is this secretly a graph? Would sorting help? Do the same subproblems keep coming up?
- Write it and test it. Walk through an example, then try the weird cases.
Key concepts to know
- Graph traversal and shortest pathsBFS, DFS and Dijkstra, and when to use each.
- Hash maps and sliding windowsSwap nested loops for a single pass.
- Heaps and priority queuesAlways have the smallest or largest item ready.
- Trees and recursionSolve tree problems by deciding what each node returns.
- Object-oriented designSplit a small program into classes that are easy to change.
- Stacks and monotonic stacksMatch brackets, parse things, and find the next bigger value in one pass.
Sources
We pulled this together from candidates' own write-ups of their interviews. They don't always agree, and things change over time.
- LeetCode Discuss: Senior SWE 4+ YOE, NYC (Nov 2025)
- LeetCode Discuss: Senior SWE, NYC (Nov 2025)
- LeetCode Discuss: Senior SWE, Pune (Nov 2025)
- LeetCode Discuss: Bloomberg phone screen, car and oasis grid
- Jointaro: Senior SWE, US (Jan 2025)
- LeetCode Discuss: SSE virtual onsite, rule-based alert system (2022)
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