private SkipListNode <TKey, TValue>[] FindRightMostNodes(TKey key)
{
var rightNodes = new SkipListNode <TKey, TValue> [maximumLevelToUse];
// Start at the top list header node
var currentNode = headNodes[CurrentListLevel];
for (var i = CurrentListLevel; i >= 0; i--)
{
while ((currentNode.Right != tail) && (comparerToUse.Compare(currentNode.Right.Key, key) < 0))
{
currentNode = currentNode.Right;
}
// Store this node - the new node will be to the right of it.
rightNodes[i] = currentNode;
// Check if there is a next level, and if there is move down.
if (i > 0)
{
currentNode = currentNode.Down;
}
}
return(rightNodes);
}
/// <summary>
/// Adds the item to the collection.
/// </summary>
/// <param name="key">The key of the item.</param>
/// <param name="value">The value to add to the colleciton.</param>
/// <remarks>
/// <b>Notes to Inheritors: </b>
/// Derived classes can override this method to change the behavior of the <see cref="Add(TKey,TValue)"/> method.
/// </remarks>
protected virtual void AddItem(TKey key, TValue value)
{
var rightNodes = FindRightMostNodes(key);
// Check if the item already exists in the list. If it does, throw an exception -
// we will not allow duplicate items here.
if ((rightNodes[0].Right != tail) && (comparerToUse.Compare(rightNodes[0].Right.Key, key) == 0))
{
throw new ArgumentException("The item is already in the list.", "key");
}
var newLevel = PickRandomLevel();
if (newLevel > CurrentListLevel)
{
for (var i = CurrentListLevel + 1; i <= newLevel; i++)
{
rightNodes[i] = headNodes[i];
}
CurrentListLevel = newLevel;
}
var newNode = new SkipListNode <TKey, TValue>(key, value)
{
Right = rightNodes[0].Right
};
// Insert the item in the first level
rightNodes[0].Right = newNode;
// And now insert the node in the rest of the levels, making sure
// to update the the links
for (var i = 1; i <= CurrentListLevel; i++)
{
var previousNode = newNode;
newNode = new SkipListNode <TKey, TValue>(key, value)
{
Right = rightNodes[i].Right
};
rightNodes[i].Right = newNode;
newNode.Down = previousNode;
}
Count++;
}
/// <param name="maximumLevel">The maximum level.</param>
/// <param name="probability">The probability.</param>
/// <param name="comparer">The comparer.</param>
/// <exception cref="ArgumentNullException"><paramref name="comparer"/> is a null reference (<c>Nothing</c> in Visual Basic).</exception>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="maximumLevel"/> is less than 1.</exception>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="probability"/> is less than 0.1.</exception>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="probability"/> is greater than 0.9.</exception>
public SkipList(int maximumLevel, double probability, IComparer <TKey> comparer)
{
#region Validation
if (maximumLevel < 1)
{
throw new ArgumentOutOfRangeException("maximumLevel", "The maximum level must be bigger than 0.");
}
Guard.ArgumentNotNull(comparer, "comparer");
if ((probability > 0.9) || (probability < 0.1))
{
throw new ArgumentOutOfRangeException("probability", "The probability must be between 0.1 and 0.9");
}
#endregion
comparerToUse = comparer;
maximumLevelToUse = maximumLevel;
probabilityToUse = probability;
// Initialise the skip list to empty nodes, and link the heads and the tails
headNodes = new SkipListNode <TKey, TValue> [maximumLevel];
headNodes[0] = new SkipListNode <TKey, TValue> {
Right = tail
};
for (var i = 1; i < maximumLevel; i++)
{
headNodes[i] = new SkipListNode <TKey, TValue> {
Down = headNodes[i - 1], Right = tail
};
//headNodes[i - 1].Up = headNodes[i];
}
}
