Status: IN
The Two Sum problem family collectively spans the lookup strategy space: hash map for O(1) complement lookup with check-before-insert ordering (classic), frequency counter for duplicate-aware pairing (III), hash set for tree-traversal membership with check-before-insert preventing self-pairing (IV), and sort plus two-pointer for inequality-bounded search (less-than-k) — demonstrating that a single problem concept exercises all major lookup mechanisms in the repo's abstraction trio.
Four Two Sum variants exercise four distinct lookup strategies spanning the repo's full abstraction trio
Depends on (SL): two-sum-complement-lookup-pattern, two-sum-iii-add-find-asymmetry, two-sum-iv-check-before-insert, two-sum-less-than-k-time-complexity