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For most mobile engineers, interviews at big tech companies come with a mix of excitement and dread. Everyone’s heard the stories — whiteboard puzzles, rapid-fire questions, endless loops. It can sound like an endurance test designed to break you.
But once you strip away the mystique, the process is predictable. It rewards structure, communication and a calm approach to problem-solving. You don’t need to be a genius — you need to prepare with purpose.
This is a practical guide for iOS engineers who want to know what to expect and how to prepare without losing their sanity.
The Loop: What You’re Walking Into
Most companies split their process into two phases.
First, you receive a screening call — usually one coding problem that serves as a yes-or-no gate. Pass it, and you’re in. Fail it, and you’re out.
Then comes the whole loop (onsite or virtual). For iOS, expect roughly:
- Two coding interviews with different people
- One system design interview
- One behavioral/culture interview
Each one tests a different part of your brain. The good news? You can prepare for all of them.
Coding: It’s Not About Speed
You’ll get 45 minutes and usually two problems, roughly 15 to 20 minutes each. Interviewers don’t care if you can type like your fingers are on fire. They care about how you think and whether you can explain it clearly.
Here’s what matters:
Ask clarifying questions before you write anything. I know it sounds obvious, but so many people just start coding immediately and end up solving the wrong problem. Spend two minutes understanding what you’re being asked. What are the constraints? What’s the input size? Are there edge cases I should worry about, like empty arrays or null strings?
Talk out loud the whole time. Seriously. Explain why you’re picking a hash map over an array, why you think recursion makes sense here and what trade-offs you’re considering. The interviewer isn’t checking whether you’re smart — they already assume that. They’re checking if they can follow your reasoning. If you go silent for 30 seconds, they get uncomfortable. If you’re talking through your process, you’re golden.
And here’s something people forget: Listen to your interviewer. If you get stuck, they’ll usually drop hints. Please pay attention to what they’re saying. “Have you thought about sorting this first?” isn’t small talk; it’s a nudge in the right direction.
Must-Have Knowledge
| Data Structure | Algorithms | Concepts |
| Array Lists | Merge Sort | Big O time |
| Hash Tables | Quick Sort | Big O space |
| Trees (Tries) | Breadth-First Search | Recursion |
| Graphs | Depth-First Search | Memoization/Dynamic Prog. |
| Stacks/Queues | Binary Search | |
| Heaps |
When you think you’re done, test it. Walk through an example. Poke at it. Find the bugs before they do. Check edge cases. What happens with an empty array? A single element? If your solution is O(n²), own it. Say it out loud and explain what could be better. But also think about space complexity. An O(n) time solution that uses O(n) space might not be better than O(n log n) time with O(1) space, depending on the problem.
If you can, mentally compile your code. Walk through it as if you were a computer. Does it work? Will it throw an error? An incomplete “optimal” solution loses to a complete, working solution that you clearly understand.
The problems themselves are not trying to trick you. You’ll see classic stuff:
Data structures: Arrays, hash tables, linked lists, trees, graphs, stacks, queues, heaps. Maybe try if you’re unlucky.
Algorithms: Sorting (merge sort, quick sort), binary search, breadth-first search, depth-first search and recursion. Sometimes it’s dynamic programming or memoization, but that’s less common for mobile roles.
Know your Big O. Both time and space. If you’re using recursion, remember it’s often O(2^n) unless you’re caching results, then it might drop to O(n). Being able to talk about complexity confidently is huge.
LeetCode medium-level problems are your sweet spot for prep. Complex problems are overkill for mobile roles. Easy ones won’t build the endurance you need. Focus on understanding the patterns, not memorizing solutions.
System Design: Show Your Thinking
This is where many mobile engineers tend to freeze up. It sounds abstract and scary. But for an iOS role, they’re not asking you to design Uber’s backend. They want to see how you think about trade-offs, scalability and architectural decisions.
You might get something like: “How would you build a photo-sharing feature?” or “Design a feed like Instagram” or “How does location tracking work in an app?”
Remember: You lead this conversation. You ask the questions. You sketch out approaches. You pick one and dig in.
Start by asking what you don’t know:
- How many users?
- What’s the usage pattern?
- What devices?
- What’s the budget?
Then think out loud. Sketch multiple approaches. Weigh the pros and cons. Pick one and go deep on it.
Talk about specific components: how data gets stored, how caching works, what happens when the network is slow, how you’d handle image processing, notifications, background sync. Use numbers. “We’re looking at maybe 50k daily active users,” or “This process runs every 15 minutes.” Numbers make it real.
For iOS specifically, know how the operating system actually works. Multithreading. Networking. Background task handling. Battery drain. App life cycle. These aren’t abstract concepts — they’re the constraints that actually matter on a phone. Showing that you understand these details demonstrates that you’re not just a generic engineer. You understand mobile.
And please, stay engaged. Don’t sit in silence while you think. Talk through your ideas. Out loud. It sounds simple, but it makes a huge difference.
Behavioral: The Part That Decides Everything
This is what most people underestimate. You can crush coding and system design, but if you seem like a nightmare to work with, you’re done.
Typical Questions You’ll Get
- “Tell me about a time you disagreed with someone.”
- “Describe a mistake you made.”
- “When did you step up and do something beyond your job description?”
What They’re Listening For
- Are you reflective?
- Do you admit when you’re wrong?
- Can you collaborate?
- Do you learn from mistakes?
- Would I want to sit next to this person for eight hours?
How To Prepare
Don’t memorize answers. That’s obvious, and it’s clear. Have real-life examples ready — four or five that showcase different aspects of you. Use a simple structure:
- Here’s the situation.
- Here’s the problem.
- Here’s what I did.
- Here’s what happened.
- Here’s what I learned.
Keep it real. Admitting you screwed up but then explaining how you fixed it is way stronger than pretending you never fail.
When they ask why you want to join, don’t say: “I’ve always dreamed of working at Big Tech Company.” That’s empty.
Say something specific and honest: “I want to work on systems that scale, with people who care about getting details right,” or “I’ve hit a ceiling on what I can learn where I am, and I want to be pushed.” Genuine beats rehearsed every single time.
How To Prepare Without Losing Your Mind
A lot of people use the 50/25/25 split:
- 50% coding practice
- 25% system design practice
- 25% behavioral prep (building your stories and getting comfortable with them)
But the thing is to make it a real routine. Don’t cram the weekend before. Pick a time each day — even 30 to 45 minutes — and actually show up to it. Track what’s hard for you. Notice patterns. If trees always trip you up, do more tree problems. If you get flustered when discussing solutions, conduct more mock interviews with actual people (not just LeetCode).
This is like training. You wouldn’t run a marathon by sprinting once a day before. It’s the same principle.
Use Your Question Time
At the end of each interview, you have the opportunity to ask questions. Please don’t waste it. In coding interviews, this is essentially a formality. But in design and behavioral rounds? Your questions can shift the vibe. They show what you care about. They make you seem like a peer, not just another candidate.
Skip the generic stuff. “What’s the culture like?” or “What does a typical day look like?” Boring. Everyone asks that. Ask something real: “What’s the biggest technical debt the team is dealing with?” or “How do you decide between refactoring and rewriting?” or “What does mentorship actually look like for new engineers here?” These questions demonstrate that you’re thinking like someone who will be part of the team, not just interviewing for a job.
The Bigger Picture
Here’s what I’ve noticed after watching people go through this: The ones who succeed aren’t the smartest in the room. They’re the ones who treat it like a project. They’re systematic. They get feedback. They iterate. They don’t memorize — they understand.
The real skill isn’t knowing the answer; it’s knowing how to find it. It’s staying methodical and precise when you’re under pressure. It’s communicating what’s in your head in a way that makes sense to someone else.
Final Thought
You probably won’t remember every algorithm or every system design principle. That’s fine. What matters is that you can think clearly, explain yourself well and show that you’re someone people actually want to work with.
The preparation sucks sometimes. But here’s the weird part: By the end of it, you’re actually a better engineer. You write cleaner code. You think about trade-offs before you code. You design with intent, rather than just building whatever comes to mind first.
Whether you land the job or not, that’s the actual win.
The post How To Prepare for Big Tech Interviews as an iOS Engineer appeared first on The New Stack.
