TopKSelector is unstable when quicksort fallback to Arrays.sort.

[Liulietong]

Related PR : #5691
The result of TopKSelector may be wrong when trim() is invoked and quiksort fallback to Arrasys.sort(). Because Arrasys.sort() is been used by mistake there.
Following test case can trigger this bug.

{
    int n = 10000;
    int k = 10000;
    int testIteration = 10;
    Random random = new Random(System.currentTimeMillis());
    for (int iter = 0; iter < testIteration; iter ++) {
      // target array to be sorted using TopKSelector
      List<Integer> target = new ArrayList<>();
      for (int i = 0; i < 9; i++) {
        List<Integer> sortedArray = new ArrayList();
        for (int j = 0; j < n; j++) {
          sortedArray.add(random.nextInt());
        }
        sortedArray.sort(Integer::compareTo);
        target.addAll(sortedArray);
      }

      TopKSelector<Integer> top = TopKSelector.least(k, Integer::compareTo);
      for (int value : target) {
        top.offer(value);
      }

      target.sort(Integer::compareTo);
      assertEquals(top.topK(), target.subList(0, k));
    }
  }

[shreelakshmijoshi]

Hi ! @Liulietong ,
I am a new open source contributor and I would love to fix the issue, could you please provide some more reference to help me understand better? Is this issue open for contribution ?

[Liulietong]

@shreelakshmijoshi I have submit the PR #5691 to fix the issue

[shreelakshmijoshi]

oh okay