/// <summary>
/// Inserts the given node into the skip list.
/// </summary>
internal void Insert(SkipListNode <T> node)
{
SkipListNode <T>[] previousNodes = new SkipListNode <T> [this.MaxLevels];
SkipListNode <T> previous = this.Head;
// find the insertion point, making use of the highest / most sparse levels first
for (int level = this.Levels - 1; level >= 0; --level)
{
while (previous.Next[level] != null && previous.Next[level].Value.CompareTo(node.Value) < 0)
{
previous = previous.Next[level];
}
if (level <= node.Levels)
{
previousNodes[level] = previous;
}
}
// Increase the skip list's level if necessary
while (this.Levels < node.Levels)
{
++this.Levels;
previousNodes[this.Levels - 1] = this.Head;
}
// Update all of the levels in the skip list to point to the new node
for (int curLevel = 0; curLevel < node.Levels; ++curLevel)
{
node.Next[curLevel] = previousNodes[curLevel].Next[curLevel];
previousNodes[curLevel].Next[curLevel] = node;
}
++this.Count;
}
public IEnumerator <T> GetEnumerator()
{
SkipListNode <T> current = this.Head.Next[0];
while (current != null)
{
yield return(current.Value);
current = current.Next[0];
}
}
/// <summary>
/// Finds the node with the given value within the skip list.
/// </summary>
/// <returns>The node with the given value, or null if no node exists.</returns>
internal SkipListNode <T> Find(T value)
{
SkipListNode <T> current = this.Head;
for (int level = this.Levels - 1; level >= 0; --level)
{
while (current.Next[level] != null && current.Next[level].Value.CompareTo(value) <= 0)
{
current = current.Next[level];
}
}
if (current != null && current.Value.CompareTo(value) == 0)
{
return(current);
}
else
{
return(null);
}
}
/// <summary>
/// Removes the node with the given value from the list.
/// </summary>
/// <returns>Returns true if a node was deleted.</returns>
public bool Delete(T value)
{
bool deleted = false;
SkipListNode <T>[] previousNodes = new SkipListNode <T> [this.Levels];
SkipListNode <T> node = this.Head;
for (int level = this.Levels - 1; level >= 0; --level)
{
while (node.Next[level] != null && node.Next[level].Value.CompareTo(value) < 0)
{
node = node.Next[level];
}
if (node.Next[level] != null)
{
previousNodes[level] = node;
}
}
node = node.Next[0];
if (node.Value.CompareTo(value) == 0)
{
for (int level = 0; level < node.Levels; ++level)
{
deleted = true;
SkipListNode <T> toDelete = previousNodes[level].Next[level];
previousNodes[level].Next[level] = toDelete.Next[level];
toDelete.Next[level] = null;
}
}
--this.Count;
return(deleted);
}
