Datadog Fulltime Software Engineer Onsite Interview Experience
Question Details
There are four rounds in total. Because I also have to work, it's scheduled for two consecutive days. The following content requires a score higher than 188. You can already view it. 1. Coding Reverse
Full Details
There are four rounds in total. Because I also have to work, it's scheduled for two consecutive days. The following content requires a score higher than 188. You can already view it. 1. Coding Reverse Index Problem Description: Given a set of strings, each string may begin with "L: " (representing Log) or "Q: " (representing Query) If it's a Query (e.g., "Q: hello world" ), it means a query is registered. You need to assign a unique qid for each different Query. If it's a Log (e.g., "L: hi hello world" ), you need to determine if this log contains all the words (in any order) of a registered query. If a match is found,
output the corresponding qid. Write a function to process this set of strings and implement the above logic. Coding Create file with buffer Each time data is written to this file, use the Write method like write("hello world"). If there is enough space in the memory buffer (buffer_size), write the data to the buffer first. Data is only written to disk when the buffer is full (by calling the flush method). Implementing write and flush should ideally be thread-safe (I didn't have one, but it was approved anyway). SD: Design a ticket discount notification system. Behavioral Questions + Project DeepDive. Standard workflow, no different from other companies. Overall, the experience was good, and the questions weren't too difficult. Please give me some points!
About This Question
This is a reported interview question from a datadog interview for a swe role during the onsite round reported in 2025.
It covers the following topics: Notification System, Strings .
Difficulty rating: Hard
Topics
More Datadog Interview Questions
About Datadog Interview Reports
This question was reported by a candidate who interviewed at Datadog. LeakCode aggregates interview reports from 10+ sources, including 1Point3Acres, Glassdoor, LeetCode Discuss, Blind, Reddit, Indeed, and Nowcoder. Each report is translated where necessary, deduplicated against existing entries, and tagged by company, role, round type, and reporting date.
Use this question as one calibration data point, not a memorization target. Companies typically rotate their question pools every 2-4 months; the exact wording of a 2024 question may differ from what you encounter today. The underlying pattern, difficulty level, and follow-up depth at Datadog are the higher-signal extractions to take from this report.
For broader preparation context, the Datadog interview process typically includes a recruiter screen, one or two technical phone screens, and a 4-5 round on-site loop covering coding, system design (at L4+ levels), and behavioral. Reports tagged on LeakCode show the round-by-round distribution and typical difficulty calibration. To browse questions filtered by round type and seniority, use the company hub linked above.
How To Practice This Type of Question
Solve similar problems on LeetCode under timed conditions (25-35 minutes per medium difficulty). The goal is pattern recognition: recognize the underlying technique (sliding window, two-pointer, BFS, memoized recursion, etc.) within 60-90 seconds of reading. Strong candidates verbalize their hypothesis out loud before coding, then iterate based on feedback. Weak candidates dive into implementation immediately, lose time on the wrong approach, and run out of time for follow-ups.
Companies update their question pools every 2-4 months. The exact wording of any given question may have been retired by the time you interview. Focus your prep on the pattern, not the specific problem. The patterns that appear in Datadog reports consistently are the ones worth investing in; one-off niche problems are not.
During Your Datadog Round
Apply the standard interview round template: clarify requirements (2-3 minutes), state your approach out loud and confirm direction with the interviewer (3-5 minutes), code with narration (15-25 minutes), test with concrete examples including edge cases (5 minutes), discuss optimization or trade-offs if time permits (5 minutes). This template is universally accepted across FAANG and adjacent companies; deviating from it produces weaker interviewer feedback signal.
The single most predictive failure mode in Datadog reports tagged "no hire": not asking clarifying questions. Interviewers are explicitly trained to weight this. Strong candidates ask 3-5 clarifying questions even on problems that look obvious; weak candidates dive into code immediately. The clarifying-question check is often the first signal recorded in the interviewer's written notes.