[Issue 15553] topN very inefficient [slower than sort, even for topN(0)] but should be O(n)

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15553

--- Comment #2 from Andrei Alexandrescu <andrei at erdani.com> ---
https://github.com/D-Programming-Language/phobos/pull/3921

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