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Rainwater Trapping Problem - solve with two-pointer technique

General/Othereasy0.2 min read

Water at i = min(left_max, right_max) - height[i]. Two pointers: maintain left_max, right_max; move from side with smaller max. Python: l,r=0,len(h)-1; lm=rm=w=0; while l<r: if h[l]<h[r]: lm=max(lm,h[l]); w+=lm-h[l]; l+=1; else: rm=max(rm,h[r]); w+=rm-h[r]; r-=1; return w. O(n)...

πŸ€– Analyze Your Answer
Frequency
Low
Asked at 1 company
Category
243
questions in General/Other
Difficulty Split
151E|43M|49H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
PayPal
Key Concepts Tested
python

Why This Question Matters

This easy-level General/Other question appears frequently in data engineering interviews at companies like PayPal. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (python) will help you answer variations of this question confidently.

How to Approach This

Start by clearly defining the core concept being asked about. Interviewers want to see that you understand the fundamentals before diving into implementation details. Structure your answer with a definition, then explain the practical application with a concise example.

Expert Answer
46 words

Water at i = min(left_max, right_max) - height[i]. Two pointers: maintain left_max, right_max; move from side with smaller max. Python: l,r=0,len(h)-1; lm=rm=w=0; while l<r: if h[l]<h[r]: lm=max(lm,h[l]); w+=lm-h[l]; l+=1; else: rm=max(rm,h[r]); w+=rm-h[r]; r-=1; return w. O(n) time, O(1) space. WHY: Two-pointer avoids extra arrays; single pass.

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According to DataEngPrep.tech, this is one of the most frequently asked General/Other interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.

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