Hot100: Trapping Rain Water (Two Pointers O(n) ACERS Guide)
Subtitle / Summary Trapping Rain Water is the classic boundary-constraint problem. This ACERS guide explains the two-pointer method, key formulas, and runnable multi-language solutions. Reading time: 12–15 min Tags: Hot100, two pointers, array SEO keywords: Trapping Rain Water, two pointers, left right max, O(n), Hot100 Meta description: Two-pointer O(n) trapped water solution with engineering scenarios and multi-language code. Target Readers Hot100 learners building core templates Engineers handling capacity/volume constraints Anyone who wants a clean O(n) solution Background / Motivation Trapped water is a proxy for “capacity under boundary constraints.” It appears in cache headroom estimation, buffer overflow analysis, and terrain capacity modeling. The naive O(n^2) method is too slow; the two-pointer approach reduces it to O(n). ...