16. Trapping Rain Water – LeetCode 42 🌧️ Two Pointers vs Prefix–Suffix | Visual & Interview-Ready!

In this episode of the LeetCode Top Interview 150 series, we solve the iconic Trapping Rain Water (LeetCode 42) problem — a must-know question that tests visualization, greedy thinking, and space optimization.

We walk through three powerful approaches, each building intuition step by step:

📊 Approach 1 — Prefix & Suffix Max Arrays
Precompute left-max and right-max boundaries to calculate trapped water at each index.
Clear logic, great for building intuition.

🧠 Approach 2 — Boundary-Based Optimization
Compute effective water levels using pre-shifted max boundaries.
A clean variation that reinforces the core idea.

💧 Approach 3 — Two Pointers (O(1) Space, Optimal)
Track left and right maximum heights while shrinking the window.
This is the most efficient and interviewer-favorite solution.

This video focuses on why the logic works, not just how — helping you internalize the pattern so you can solve any variation under interview pressure.

Perfect for FAANG prep, DSA mastery, and anyone following the LeetCode 150 roadmap.

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