GUIDED PRACTICE

Prefix sums

Turn range calculations into subtraction.

A AceYourInterviews editorial · 10 min study

10:00Self-guided practice timer

The timer resets when you leave this page. Save your design separately.

Your challenge

Why must the map initially contain prefix sum zero once?

Your design draft

Clarify assumptions, explain your approach, and test the difficult cases. Save your draft, then compare it with the study notes.

Self-review checklist

I clarified the requirements and constraints.I explained why the approach works.I considered failures, boundaries, and alternatives.I identified one improvement for my next attempt.

Self-guided practice. Automated AI feedback and code execution are not connected.