LC 36
Valid Sudoku
Medium · LC 1–100
Candidate solution routes
Primary
FreeConstraint-satisfaction backtracking
Invariant: At recursion entry, the partial assignment satisfies every activated constraint and every auxiliary set/count exactly matches it; a pruned branch has no legal completion.
candidate confidence: 0.540 · 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.