LC 9
Palindrome Number
Easy · LC 1–100
Candidate solution routes
Primary
FreeOpposite-Direction Two Pointers
Invariant: Every uneliminated pair uses endpoints inside [l,r]; a moved endpoint is proven unable to pair with any remaining opposite endpoint to satisfy the goal.
candidate confidence: 0.360 · 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.