Hot100: First Missing Positive In-Place Index Placement ACERS Guide
Subtitle / Summary First Missing Positive is a classic in-place indexing problem. Place each valid value x into slot x-1, then scan for the first mismatch. This ACERS guide explains the derivation, invariant, pitfalls, and production-style transfer. Reading time: 12-15 min Tags: Hot100, array, in-place hashing SEO keywords: First Missing Positive, in-place hashing, index mapping, O(n), Hot100, LeetCode 41 Meta description: O(n)/O(1) solution for First Missing Positive using in-place index placement, with complexity analysis, engineering scenarios, and runnable multi-language code. Target Readers Hot100 learners building stable array templates Intermediate developers who want to master in-place indexing techniques Engineers who need linear-time, constant-space array normalization Background / Motivation “Find the smallest missing positive” is fundamentally a placement problem. ...