/// <summary>
/// IComparable method implementation
/// </summary>
public int CompareTo(SkipListNode <T> other)
{
if (other == null)
{
return(-1);
}
return(this.Value.CompareTo(other.Value));
}
/// <summary>
/// CONSTRUCTORS
/// </summary>
public SkipListNode(T value, int level)
{
if (level < 0)
{
throw new ArgumentOutOfRangeException("Invalid value for level.");
}
Value = value;
Forwards = new SkipListNode <T> [level];
}
/// <summary>
/// CONSTRUCTOR
/// </summary>
public SkipList()
{
_count = 0;
_currentMaxLevel = 1;
_randomizer = new Random();
_firstNode = new SkipListNode <T>(default(T), MaxLevel);
for (int i = 0; i < MaxLevel; ++i)
{
_firstNode.Forwards[i] = _firstNode;
}
}
/// <summary>
/// Remove an element from list and then return it
/// </summary>
public bool Remove(T item, out T deleted)
{
// Find the node in each of the levels
var current = _firstNode;
var toBeUpdated = new SkipListNode <T> [MaxLevel];
// Walk after all the nodes that have values less than the node we are looking for.
// Mark all nodes as toBeUpdated.
for (int i = _currentMaxLevel - 1; i >= 0; --i)
{
while (current.Forwards[i] != _firstNode && current.Forwards[i].Value.IsLessThan(item))
{
current = current.Forwards[i];
}
toBeUpdated[i] = current;
}
current = current.Forwards[0];
// Return default value of T if the item was not found
if (current.Value.IsEqualTo(item) == false)
{
deleted = default(T);
return(false);
}
// We know that the node is in the list.
// Unlink it from the levels where it exists.
for (int i = 0; i < _currentMaxLevel; ++i)
{
if (toBeUpdated[i].Forwards[i] == current)
{
toBeUpdated[i].Forwards[i] = current.Forwards[i];
}
}
// Decrement the count
--_count;
// Check to see if we've deleted the highest-level node
// Decrement level
while (_currentMaxLevel > 1 && _firstNode.Forwards[_currentMaxLevel - 1] == _firstNode)
{
--_currentMaxLevel;
}
// Assign the deleted output parameter to the node.Value
deleted = current.Value;
return(true);
}
/// <summary>
/// Adds item to the list
/// </summary>
public void Add(T item)
{
var current = _firstNode;
var toBeUpdated = new SkipListNode <T> [MaxLevel];
for (int i = _currentMaxLevel - 1; i >= 0; --i)
{
while (current.Forwards[i] != _firstNode && current.Forwards[i].Value.IsLessThan(item))
{
current = current.Forwards[i];
}
toBeUpdated[i] = current;
}
current = current.Forwards[0];
// Get the next node level, and update list level if required.
int lvl = _getNextLevel();
if (lvl > _currentMaxLevel)
{
for (int i = _currentMaxLevel; i < lvl; ++i)
{
toBeUpdated[i] = _firstNode;
}
_currentMaxLevel = lvl;
}
// New node
var newNode = new SkipListNode <T>(item, lvl);
// Insert the new node into the skip list
for (int i = 0; i < lvl; ++i)
{
newNode.Forwards[i] = toBeUpdated[i].Forwards[i];
toBeUpdated[i].Forwards[i] = newNode;
}
// Increment the count
++_count;
}