This year, the competition for DoorDash internships was truly fierce. Several of my classmates applied to over a dozen top companies, and those who ultimately received DoorDash interview invitations were basically top performers with algorithm scores of 200+, introductory system design skills, and the ability to explain business concepts in their self-introductions. So when I received my interview invitation, it felt like unlocking a hidden challenge: exciting, but knowing it wouldn't be easy. Below, I'll discuss each question I encountered, how the interviewer followed up, and how I responded, hoping to give those preparing for DoorDash 26NG a heads-up.
Round 1: Algorithmic Interview - Interviewer comes up with a sentence:
"If you were a dasher starting from this location... how fast can you find the closest restaurant?"
When I heard it, I thought, "Oh, I'm sure it's BFS." But the interviewer was very realistic. But the interviewer spoke very life-like:
He pulls out a small grid (desensitized):
- 0 Yes Road
- X is the wall.
- R is for Restaurant
- S is the starting point for dasher.
Then he said something very DoorDash:
"Imagine you're hungry and you're on a bike. Where's the closest food?"
I laughed out loud and went straight to work on BFS, explaining as I wrote the code that I would use queue spreading and visited to prevent duplicates.
Halfway through writing he interjects:
"Why BFS instead of DFS?"
I'll go along with this and say that BFS searches by floor and the first time you come across a restaurant is the closest distance.
The interviewer nods, "Good. that's exactly what we do in routing."
That's when I realized that DoorDash's algorithmic problems aren't meant to torture you, they're meant to see if you can apply graph theory to real business.
Round 2: Algorithm + Matching Logic
The interviewer was more like throwing me into a real dispatch center this round.
He gave two lists (desensitized narratives):
- Stack of Orders: Includes Location & Lead Time
- A stack of dasher: contains current position & idle state
Then he asked me:
"Suppose you're running the dispatch system right now.
How do you assign dashers to minimize delivery time?"
I was going to talk about an optimal match, but he said:
"We don't need optimal. We need fast and scalable."
DoorDash that flavor coming up:execution > theoretical optimization.
I'll talk about three:
- greedy (find the nearest available dasher per order)
- Weighted scoring function (distance + prep time + dasher rating)
- Limit search area (sub-zones, no global matching)
The interviewer immediately followed up:
"Why zone-based?"
"What if a dasher is idle just across the border?"
I'll talk about business tradeoffs: full-map matching is too slow, zone is the most stable; cross-zone idle can be triggered by thresholds.
He came after listening:
"This is close to how our dispatch system thinks."
At that moment, it was really cool. I felt that I was not doing a question, but discussing a real product.
Round 3: System Design - The first time I was asked to "track a rider in real time."
This round was a classic DoorDash question, but the interviewer spoke very graphically.
He asked me to visualize it directly:
"You're ordering bubble tea.
Your dasher is on a scooter updating GPS every 3 seconds.
Show me how you'd build the real-time tracking."
I brainstormed an animation of Milk Tea on the Road on the spot and started building the frame:
- WebSocket: real-time push client
- Redis: Only the latest position is stored (no history)
- Location Service: do throttle + de-jitter
- Sharding: by region scale
- Front-end: Subscription order-specific channel
Then he asked:
"What if a million users are watching riders at the same time?"
I'll talk about fan-out, pub/sub, and making channels by order ID.
The interviewer was pleased:
"You're thinking like a real-time system engineer."
For the first time, I thought that it was possible for an intern to talk about this level of system.
Round 4: Ordering System Design - The Most Asked Question
The interviewer's opening statement for this question was particularly like a real incident:
"A user taps 'Place Order'...
but the network glitches.
They tap again.
We get two payments.
What do we do?"
All I could think of was one word:idempotency.
I speak:
- Each time an order is placed a requestId
- server Check for duplicates
- Order Service + Payment Service to ensure atomic
- Unsuccessful payment to rollback order
- Retry-safe for packet loss scenarios
The interviewer nodded:
"Exactly. Most issues in order placement come from duplicated requests."
I totally get it after hearing that:
DoorDash's system design questions are never abstract, but come directly from actual on-line incidents.
Round 5: Behavioral - More important here than I thought!
DD's behavioral interview was asked with a great sense of logic and without formality.
The three most critical questions:
Why DoorDash?
I speak:
I like real-time, I like route optimization, I like systems that are connected to the real world.
And mentioned that I've done small projects related to maps and paths.
The interviewer understood in seconds that I was genuinely interested in the field and not just pitching.
② Collaboration Have you ever led a pit yourself?
I told a story:
When I was doing a side project, my teammate and I didn't agree on the structure of the API interface, and I ended up writing both solutions as prototypes, comparing performance and maintainability with real data.
In the end we adopted the more appropriate version.
The interviewer especially liked hearing "making decisions with prototype".
③ How to face the fast-paced environment?
I said I was used to checklist and writing to minimize context switches.
They eat it up - DD The pace is really fast.
Final Summary: DoorDash looks at "Can you move right now?"
The deepest lesson I learned after facing around is this:
DoorDash doesn't roll with puzzles or fancy architectures.
They rolled it:
- Can you take the problem apart quickly?
- Can you do tradeoffs from a business perspective
- Can you get up to speed quickly when you encounter something new
- There's no sense of real-time logistics.
I'm preparing for system design & behavioral this time, and I'm getting a VO voice assist from Programhelp.
Interviews were hounded: quick nudges to wake up to key points, reminders of tradeoffs, helping me tell the story more like "making decisions on the spot."
It's time to add an "ultimate insurance policy" to your interviews
Made it to VO? Congrats you are one step away from a big package! But DD's System Design is really not NG friendly and Coding is stressful. Don't want to drop the chain at the last minute? DoorDash VO full-process untraceable assists : Senior tutors are online in real time, and Coding + System Design is escorting you throughout the whole process. Safe, hidden, efficient, help you get the Offer steadily. Don't hesitate, the opportunity of 26NG does not wait for anyone.
