Algorithm practice prepares you for only one round of the FDE interview loop

Picture this: you have solved a few hundred LeetCode problems and you walk into an FDE interview. The interviewer says: “A chain of clinics wants to use AI to cut patient waiting times. Where do you start?” There is no input, no output and no complexity constraint.

An FDE interview guide on techinterview.org puts it bluntly: if you only practise algorithms, you are studying for the least important part of the exam. Educative’s FDE course describes a loop of four rounds: decomposition, customer simulation, a technical round and a customer-facing behavioural round.

Of those four, algorithm practice mainly helps with the technical round.

Databricks is the clearest example. According to Aced’s guide to the company’s FDE role, the decomposition round runs about 60 minutes, candidates must design a system from a vague business goal, and the round is treated as the centrepiece of the loop. Coding is a separate 60-minute round.

If you want to become an FDE, decomposition is the skill most worth practising seriously.

Why is the interview mostly conversation?

The answer lies in the job itself. Anthropic’s FDE job posting describes working directly with strategic customers and frequent travel, 25–50% of the time, to customer sites to build alongside them.

The posting also asks for a high degree of ownership and the ability to handle ambiguity inside complex organisations.

No customer hands an FDE a complete spec. The techinterview.org guide explains that the interview simulates exactly that situation, which is why most of the time is spent talking rather than typing.

The decomposition format was created and popularised by Palantir, to see whether candidates can find their way when nobody has drawn them a map.

What are interviewers actually listening for?

Interviewers work from a fairly specific rubric. According to techinterview.org, they score four things: structured decomposition, empathy for the end user, reasoning about data, and judgement on scope. Educative’s course sums up the purpose of the round as testing whether you tackle an ambiguous problem systematically.

These four criteria also explain the most common mistake Aced records: jumping straight to a solution. A candidate hears the prompt and immediately says “I’d use RAG with a vector database”. At that point they have skipped the end user, not asked where the data lives and not cut the scope. Three of the four criteria are lost before the interview has properly begun.

A worked session: from “reduce waiting time” to a design

Go back to the clinic prompt above. The Databricks guide advises spending the first 5–15 minutes clarifying the goal before moving on to technical design. Below is a hypothetical script for those opening minutes.

Candidate: “Before I design anything, can I check: does ‘waiting time’ mean from booking to the appointment, or from arriving at the front desk to seeing the doctor?”

Interviewer: “Time spent sitting in the waiting room.”

Candidate: “Who is most affected by this: patients, receptionists or clinic managers? And how do receptionists decide the order of appointments today?”

The second question shows empathy for the end user. You are looking for the person who will use the system every day, not just the person who signs the contract. Next comes data:

Candidate: “Does the clinic record check-in time, consultation start time and service type? Is that in management software or on paper?”

If the answer is “yes, in the management software, about two years of it”, you have grounds to reason about a model that predicts consultation length. If it is “on paper”, the first phase of the project has to be data collection, and you need to say so explicitly.

Finally comes scope, the part many candidates forget:

Candidate: “I’d propose that phase one covers a single clinic and only predicts consultation length, so receptionists can tell patients how long they’ll wait. Automatic rescheduling waits until phase two, once we’ve measured whether the predictions are accurate. Does that sound reasonable?”

Only after ten minutes or so of this do you draw the architecture: data sources, pipeline, model, an interface for receptionists, and how success will be measured. By now every box in the design has a reason behind it, and the interviewer has heard all four criteria.

In what order should you practise?

Repeat a fixed sequence until it becomes a reflex. First, restate the goal in your own words and ask how “success” will be measured. Next, identify the end user and how they work today. Then ask where the data lives, what its quality is and who owns it.

Once you have those three pieces, propose a small scope that can be delivered in a few weeks and say clearly which parts you are deliberately leaving out. Only then draw the architecture, and finish with how you will measure the result.

Throughout the session, keep checking with the interviewer that you are heading in the right direction, because the round is designed to be collaborative, not a monologue.

If spoken English is not your strength, do not practise only on paper. Practise out loud, against a timer, because the round asks you to think aloud and does not grade your notes.

One tip when reading job descriptions: if a posting stresses handling ambiguity and working directly with customers, as Anthropic’s does, expect the conversational part to be heavy and put more hours into decomposition practice.

The familiar traps

The first trap is treating clarifying questions as a formality: asking three questions for show and then presenting the architecture you had in mind from the start. Interviewers notice immediately when their answers do not change your design.

The second trap is taking on the whole scope. Trying to solve the entire problem in 60 minutes means leaving the scope-judgement criterion in the techinterview.org rubric blank. The third trap is thinking in silence.

The round requires you to talk, so a minute of silence is a minute in which the interviewer has nothing to score.

The coding round still needs preparation, but it only proves you can write code. The decomposition round shows whether you know what code to write, and for whom. In a job where you must find your own way through a customer’s ambiguity, that is where your practice hours are best spent.