LC 77
Combinations
Medium · LC 1–100
Candidate solution routes
Primary
FreeSubset / combination backtracking
Invariant: On entering dfs(start), path indices are strictly increasing and already fixed below start. The call generates exactly completions whose next index is at least start, preventing duplicate orders.
candidate confidence: 0.740 · metadata_only
Alternate 1
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: 0.610 · 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.