Design
Stopwatch & Lap Timer
Design a stopwatch application supporting start, pause, resume, reset, and lap recording.
This is a Low-Level Design (LLD) problem. New to LLD vs HLD? Start here.
01 - Why interviewers ask this
It looks trivial but catches candidates who accumulate time via ticking counters — interviewers use it to see if you compute elapsed time from timestamps instead, which is the actually-correct approach.
02 - Where this system exists in the real world
You interact with this design every day.
Fitness and workout timer apps
Sports lap-timing systems
Productivity/Pomodoro timer tools
03 - What you'll master
Solve this once. Know it forever.
Compute elapsed time from timestamps, not tick counters
Model pause/resume without time drift
Track and rank lap splits
04 - What you'll design
6 functional · 2 non-functional requirements.
Start the stopwatch from zero
5 more requirements inside
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05 - Companies that ask this
You may face this exact question in your next interview.
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