/// <summary>
/// Sort the top K element from an array, using floyd build heap.
/// it will not modify the input.
/// <remark>
/// Complexity expected to be:
/// O(k+(n-k)Log(k)) => O(nlog(k))
/// </remark>
/// </summary>
/// <param name="len"></param>
/// <param name="k"></param>
/// <returns></returns>
public static T[] TopKSortDoubleArrayUsingBinaryHeap <T>(T[] arr, int k)
where T : IComparable <T>
{
if (k <= 0 || arr == null || arr.Length == 0)
{
return(null);
}
k = k >= arr.Length ? arr.Length : k;
IPriorityQ <T> q = new SimpleBinaryHeap <T>(arr, 0, k);
for (int i = k; i < arr.Length; i++)
{
T element = arr[i];
if (element.CompareTo(q.Peek()) > 0)
{
q.RemoveMin();
q.Enqueue(element);
}
}
T[] res = new T[k];
for (int i = 0; i < k; i++)
{
res[i] = q.RemoveMin();
}
return(res);
}
public void TestPartialFloydBuildHeap()
{
int[] randomarr = GetRandomizedIntSequence(100);
IPriorityQ <int> q = new SimpleBinaryHeap <int>(randomarr, 90, 9);
int pre = q.RemoveMin();
while (q.Size != 0)
{
Assert.IsTrue(q.Peek() > pre);
pre = q.RemoveMin();
}
}