Trapping Rain Water (LC 42)

Problem Overview

Citadel asked LeetCode 42, Trapping Rain Water, in phone screens. The reports give only the problem number, so the statement below is the public LeetCode one. Given n non-negative integers representing an elevation map where each bar has width 1, compute how much water it can trap after raining. What…

• 1 candidate-reported follow-up — the exact probes interviewers asked, with the trigger for each
• The rest of the problem statement — full requirements, constraints, and edge cases
• Approach and trade-offs — what passing candidates did, and the mistakes that sink people