private SkipListNode <TKey, TValue>[] FindRightMostNodes(TKey key)
{
var rightNodes = new SkipListNode <TKey, TValue> [_maxLevelToUse];
// Start at the top list header node
var currentNode = _headNodes[_currentLevel];
for (var i = _currentLevel; 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>
/// Gets the enumerator.
/// </summary>
/// <returns>An enumerator for enumerating though the collection.</returns>
public IEnumerator <KeyValuePair <TKey, TValue> > GetEnumerator()
{
// Start at the bottom level and add all the keys to the return array.
SkipListNode <TKey, TValue> startNode = _headNodes[0];
while (startNode.Right != _tail)
{
startNode = startNode.Right;
yield return(new KeyValuePair <TKey, TValue>(startNode.Key, startNode.Value));
}
}
/// <summary>
/// Adds the specified key.
/// </summary>
/// <param name="key">The key.</param>
/// <param name="value">The value.</param>
public void Add(TKey key, TValue value)
{
var rightNodes = FindRightMostNodes(key);
// Check if the item allready 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(Resources.ItemAlreadyInList);
}
var newLevel = PickRandomLevel();
if (newLevel > _currentLevel)
{
for (var i = _currentLevel + 1; i <= newLevel; i++)
{
rightNodes[i] = _headNodes[i];
}
_currentLevel = 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 <= _currentLevel; i++)
{
var previousNode = newNode;
newNode = new SkipListNode <TKey, TValue>(key, value)
{
Right = rightNodes[i].Right
};
rightNodes[i].Right = newNode;
newNode.Down = previousNode;
}
_itemsCount++;
}
/// <summary>
/// Initializes a new instance of the <see cref="SkipList<TKey, TValue>"/> class.
/// </summary>
/// <param name="maxLevel">The max level.</param>
/// <param name="probability">The probability.</param>
/// <param name="comparer">The comparer.</param>
public SkipList(int maxLevel, double probability, IComparer <TKey> comparer)
{
if (maxLevel < 1)
{
throw new ArgumentOutOfRangeException("maxLevel", maxLevel, Resources.MaximumLevelBiggerThan0);
}
if (comparer == null)
{
throw new ArgumentNullException("comparer");
}
if ((probability > 0.9) || (probability < 0.1))
{
throw new ArgumentOutOfRangeException("probability", probability, Resources.InvalidProbability);
}
_comparerToUse = comparer;
_maxLevelToUse = maxLevel;
_probabilityToUse = probability;
// Initialise the skip list to empty nodes, and link the heads and the tails
_headNodes = new SkipListNode <TKey, TValue> [maxLevel];
_headNodes[0] = new SkipListNode <TKey, TValue>
{
Right = _tail
};
for (var i = 1; i < maxLevel; i++)
{
_headNodes[i] = new SkipListNode <TKey, TValue>
{
Down = _headNodes[i - 1], Right = _tail
};
//headNodes[i - 1].Up = headNodes[i];
}
}
