LC 41
First Missing Positive
Hard · LC 1–100
Candidate solution routes
Primary
FreeBinary-Search Boundary / First True
Invariant: The first True always lies in [lo,hi]; indexes left of lo are proven False, while hi remains a feasible candidate.
candidate confidence: 0.418 · metadata_only
Alternate 1
FreePrefix State plus Hash Frequency
Invariant: Before processing position i, the table contains exactly the historical prefixes allowed as left boundaries; query-before-insert avoids using a future or self state accidentally.
candidate confidence: 0.368 · metadata_only
How to use this page
Read the statement and constraints first, then validate recognition signals, invariant, and complexity. Candidate score is not correctness evidence.