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Make ExceptWith linear on InsertionOrderSet, OrderedSet and ContiguousSet [patch] - #144
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…sSet [patch] ExceptWith removed one element at a time, and each removal shifted the list or array tail, so excepting m elements from an n-element set was O(n·m): seconds at 80k elements. It now builds one lookup from `other` with the set's own comparer and compacts the storage in a single pass, as IntersectWith and SymmetricExceptWith already do. Survivors keep their order, and ExceptWith(self) still empties the set. Adds a large-set timing test per type and an ExceptWith benchmark. Fixes #108 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017vfJW6AfToAg6F8bcZwwZ5
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Fixes #108
What was wrong
ExceptWithremoved elements one at a time from list- or array-backed storage, and each removal shifted the tail. Excepting m elements from an n-element set therefore cost O(n·m).IntersectWithandSymmetricExceptWithhad already been changed to compact in one pass, which closed the other rows of the issue's table, butExceptWithwas still per-element on all three types.Change
Each
ExceptWithbuilds one lookup fromother, using the set's own comparer, and then compacts the storage in a single pass:InsertionOrderSet<T>HashSet<T>items.RemoveAll, which also drops each removed item from the uniqueness indexContiguousSet<T>HashSet<T>RemoveWhere, which clears vacated slots and bumpsversiononly when something was removedOrderedSet<T>ToComparerSet, which reusesotherwhen it is anOrderedSetwith the same compareritems.RemoveAllThe surviving elements keep their order.
ExceptWith(self)keeps its earlyClear(). AnExceptWiththat removes nothing still leaves the version unchanged, so it doesn't invalidate a running enumeration.Tests
*_RunsInLinearTimepattern. Each also checks that the survivors come out in order.InsertionOrderSetTests.ExceptWith_LargeSetRemovingEvens_…(200k)ContiguousSetTests.ExceptWith_LargeSetRemovingEvens_…(100k)OrderedSetTests.ExceptWith_LargeEvens_…(800k)OrderedSetneeds the larger size because aList.RemoveAtshift is a fast memmove: at 400k the old code still finished in 3.8 s.Containers.Testsuite: 519 passed, 0 failed.SetExceptWithBenchmarksclass (10k and 80k elements,HashSet<T>as the baseline), which the acceptance criteria asked for. I built it but didn't run it.🤖 Generated with Claude Code
https://claude.ai/code/session_017vfJW6AfToAg6F8bcZwwZ5