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sort: TestAdversary is broken #21581

tom93 opened this issue Aug 24, 2017 · 1 comment

sort: TestAdversary is broken #21581

tom93 opened this issue Aug 24, 2017 · 1 comment


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@tom93 tom93 commented Aug 24, 2017

There are some major problems with TestAdversary (based on A Killer Adversary for Quicksort by M. D. McIlroy).

  1. The data field is modified by Swap() but ignored by Less(), so swapping has no effect.

  2. Less() compares elements using >=, which is messed up.

  3. The test never checks anything, so it will always pass. It should count the number of comparisons and fail if there are too many.

  4. The size 100 is too small to distinguish between O(n^2) with a small constant factor and O(n*log(n)).

  5. (nitpicking) map[int]int can be replaced with []int, which is much more efficient.

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@gopherbot gopherbot commented Aug 24, 2017

Change mentions this issue: sort: fix TestAdversary

@gopherbot gopherbot closed this in 3723d08 Aug 25, 2017
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