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Eightfold.AI Lead Backend (SDE-3) Interview Experience

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eightfold.ai
· Lead Backend (SDE-3) Engineer
March 23, 2026 · 1 reads

Summary

I interviewed for a Lead Backend (SDE-3) Engineer role at Eightfold.AI, which involved discussions on past projects, behavioral questions, a coding problem on stream processing for unique elements, and a system design problem.

Full Experience

Sharing my interview experience for SDE-3(lead) engineer role at Eightfold.ai

Round 1: HM

Mostly discussed around past projects, your contribution and behavioral questions

Round 2: Coding + HLD

You receive strings one by one from a stream.

After each insertion, you must output:

the oldest string that has appeared exactly once so far

If no such string exists, return ""

Example

Stream:
a, b, a, c, b, d
After each insert:
insert a → oldest non-repeating = a
insert b → a
insert a → b
insert c → b
insert b → c
insert d → c
Output:
a, a, b, b, c, c

For HLD : Design Notification Service.

Interview Questions (2)

1.

Oldest Non-Repeating String in Stream

Data Structures & Algorithms

You receive strings one by one from a stream.

After each insertion, you must output:

the oldest string that has appeared exactly once so far

If no such string exists, return ""

Example

Stream: a, b, a, c, b, d After each insert: insert a → oldest non-repeating = a insert b → a insert a → b insert c → b insert b → c insert d → c Output: a, a, b, b, c, c

2.

Design Notification Service

System Design

Design Notification Service.

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