/// <summary>
/// Rearranges the array so that a[k]} contains the kth smallest key;
/// a[0] through a[k-1] are less than (or equal to) a[k];
/// a[k+1] through a[n-1] are greater than (or equal to) a[k].
/// </summary>
/// <param name="a">the array</param>
/// <param name="k">the rank of the key</param>
/// <returns>the key of rank k}</returns>
public static T Select(T[] a, int k)
{
if (k < 0 || k >= a.Length)
{
throw new ArgumentOutOfRangeException(nameof(k), k, "out of bounds");
}
StdRandom.shuffle(a);
int lo = 0, hi = a.Length - 1;
while (hi > lo)
{
int i = partition(a, lo, hi);
if (i > k)
{
hi = i - 1;
}
else if (i < k)
{
lo = i + 1;
}
else
{
return(a[i]);
}
}
return(a[lo]);
}
/// <summary>
/// Randomized insertion.
/// make new node the root with uniform probability
/// </summary>
/// <param name="x"></param>
/// <param name="key"></param>
/// <param name="val"></param>
/// <returns></returns>
internal override BaseNode <TKey, TValue> PutKey(BaseNode <TKey, TValue> x, TKey key, TValue val)
{
if (x == null)
{
return(new BaseNode <TKey, TValue>(key, val, 1));
}
int cmp = key.CompareTo(x.key);
if (cmp == 0)
{
x.val = val;
return(x);
}
if (StdRandom.bernoulli(1.0 / (x.Size + 1.0)))
{
return(PutRoot(x, key, val));
}
if (cmp < 0)
{
x.left = PutKey(x.left, key, val);
}
else
{
x.right = PutKey(x.right, key, val);
}
x.UpdateSize();
return(x);
}
/// <summary>
/// Rearranges the array in ascending order, using the natural order.
/// </summary>
/// <param name="a">the array to be sorted</param>
public static void Sort(T[] a)
{
StdRandom.shuffle(a);
sort(a, 0, a.Length - 1);
Debug.Assert(SortingHelper <T> .isSorted(a));
}
/// <summary>
/// Randomized deletion.
/// </summary>
/// <param name="a"></param>
/// <param name="b"></param>
/// <returns></returns>
private BaseNode <TKey, TValue> joinLR(BaseNode <TKey, TValue> a, BaseNode <TKey, TValue> b)
{
if (a == null)
{
return(b);
}
if (b == null)
{
return(a);
}
if (StdRandom.bernoulli((double)a.Size / (a.Size + b.Size)))
{
a.right = joinLR(a.right, b);
a.UpdateSize();
return(a);
}
else
{
b.left = joinLR(a, b.left);
b.UpdateSize();
return(b);
}
}
