/// <summary>
/// Removes the element with the specified key from the SkipList.
/// </summary>
/// <param name="key">
/// The key of the element to remove.
/// </param>
public void Remove(object key)
{
SkipListNode[] update = new SkipListNode[MaxLevel];
SkipListNode curr;
if (Search(key, out curr, update))
{
// Take the forward references that point to the node to be
// removed and reassign them to the nodes that come after it.
for (int i = 0; i < listLevel &&
update[i].forward[i] == curr; i++)
{
update[i].forward[i] = curr.forward[i];
}
curr.Dispose();
// After removing the node, we may need to lower the current
// skip list level if the node had the highest level of all of
// the nodes.
while (listLevel > 1 && nillNode.forward[listLevel - 1] == nillNode)
{
listLevel--;
}
// Keep track of the number of nodes.
count--;
// Indicate that the skip list has changed.
version++;
}
}
/// <summary>
/// Gets or sets the element with the specified key. This is the
/// indexer for the SkipList.
/// </summary>
public object this[object key]
{
get
{
object val = null;
SkipListNode curr;
if (Search(key, out curr))
{
val = curr.entry.Value;
}
return(val);
}
set
{
SkipListNode[] update = new SkipListNode[MaxLevel];
SkipListNode curr;
// If the search key already exists in the skip list.
if (Search(key, out curr, update))
{
// Replace the current value with the new value.
curr.entry.Value = value;
// Indicate that the skip list has changed.
version++;
}
// Else the key doesn't exist in the skip list.
else
{
// Insert the key and value into the skip list.
Insert(key, value, update);
}
}
}
public void Add(T value)
{
SkipListNode <T>[] updates = this.BuildUpdateList(value);
SkipListNode <T> current = updates[0];
if (current[0] != null && current[0].Value.CompareTo(value) == 0)
{
return;
}
SkipListNode <T> n = new SkipListNode <T>(value, this.ChooseRandomHeight(this.Height + 1));
this.Count++;
if (n.Height > this.Height)
{
this.Head.IncrementHeight();
this.Head[this.Head.Height - 1] = n;
}
for (int i = 0; i < n.Height; i++)
{
if (i < updates.Length)
{
n[i] = updates[i][i];
updates[i][i] = n;
}
}
}
public bool Contains(T value)
{
SkipListNode <T> curent = this.Head;
for (int i = this.Height - 1; i >= 0; i--)
{
while (curent[i] != null)
{
if (curent[i].Value.CompareTo(value) == 0)
{
return(true);
}
else if (curent[i].Value.CompareTo(value) < 0)
{
curent = curent[i];
}
else
{
break;
}
}
}
return(false);
}
public bool Remove(T value)
{
SkipListNode <T>[] updates = this.BuildUpdateList(value);
SkipListNode <T> current = updates[0][0];
if (current != null && current.Value.CompareTo(value) == 0)
{
this.Count--;
for (int i = 0; i < this.Head.Height; i++)
{
if (updates[i][i] != current)
{
break;
}
else
{
updates[i][i] = current[i];
}
}
if (this.Head[this.Height - 1] == null)
{
this.Head.DecrementHeight();
}
return(true);
}
else
{
return(false);
}
}
/// <summary>
/// Searches for the specified key.
/// </summary>
/// <param name="key">
/// The key to search for.
/// </param>
/// <returns>
/// Returns true if the specified key is in the SkipList.
/// </returns>
private bool Search(object key)
{
SkipListNode curr;
SkipListNode[] dummy = new SkipListNode[MaxLevel];
return(Search(key, out curr, dummy));
}
/// <summary>
/// Search for the specified key using the IComparable interface
/// implemented by each key.
/// </summary>
/// <param name="key">
/// The key to search for.
/// </param>
/// <param name="curr">
/// A SkipList node to hold the results of the search.
/// </param>
/// <param name="update">
/// An array of nodes holding references to the places in the SkipList
/// search in which the search dropped down one level.
/// </param>
/// <returns>
/// Returns true if the specified key is in the SkipList.
/// </returns>
/// <remarks>
/// Assumes each key inserted into the SkipList implements the
/// IComparable interface.
///
/// If the specified key is in the SkipList, the curr parameter will
/// reference the node with the key. If the specified key is not in the
/// SkipList, the curr paramater will either hold the node with the
/// first key value greater than the specified key or null indicating
/// that the search reached the end of the SkipList.
/// </remarks>zx
private bool SearchWithComparable(object key, out SkipListNode curr,
SkipListNode[] update)
{
// Make sure key is comparable.
if (!(key is IComparable))
{
string msg = resManager.GetString("ComparableError");
throw new ArgumentException(msg);
}
bool found = false;
IComparable comp;
// Begin at the start of the skip list.
curr = nillNode;
// Work our way down from the top of the skip list to the bottom.
for (int i = listLevel - 1; i >= 0; i--)
{
// Get the comparable interface for the current key.
comp = (IComparable)curr.forward[i].entry.Key;
// While we haven't reached the end of the skip list and the
// current key is less than the search key.
while (curr.forward[i] != nillNode && comp.CompareTo(key) < 0)
{
// Move forward in the skip list.
curr = curr.forward[i];
// Get the comparable interface for the current key.
comp = (IComparable)curr.forward[i].entry.Key;
}
// Keep track of each node where we move down a level. This
// will be used later to rearrange node references when
// inserting a new element.
update[i] = curr;
}
// Move ahead in the skip list. If the new key doesn't already
// exist in the skip list, this should put us at either the end of
// the skip list or at a node with a key greater than the search key.
// If the new key already exists in the skip list, this should put
// us at a node with a key equal to the search key.
curr = curr.forward[0];
// Get the comparable interface for the current key.
comp = (IComparable)curr.entry.Key;
// If we haven't reached the end of the skip list and the
// current key is equal to the search key.
if (curr != nillNode && comp.CompareTo(key) == 0)
{
// Indicate that we've found the search key.
found = true;
}
return(found);
}
/// <summary>
/// Copies the elements of the SkipList to an Array, starting at a
/// particular Array index.
/// </summary>
/// <param name="array">
/// The one-dimensional Array that is the destination of the elements
/// copied from SkipList.
/// </param>
/// <param name="index">
/// The zero-based index in array at which copying begins.
/// </param>
public void CopyTo(Array array, int index)
{
// Make sure array isn't null.
if (array == null)
{
string msg = resManager.GetString("NullArrayCopyTo");
throw new ArgumentNullException(msg);
}
// Make sure index is not negative.
else if (index < 0)
{
string msg = resManager.GetString("BadIndexCopyTo");
throw new ArgumentOutOfRangeException(msg);
}
// Array bounds checking.
else if (index >= array.Length)
{
string msg = resManager.GetString("BadIndexCopyTo");
throw new ArgumentException(msg);
}
// Make sure that the number of elements in the skip list is not
// greater than the available space from index to the end of the
// array.
else if ((array.Length - index) < Count)
{
string msg = resManager.GetString("BadIndexCopyTo");
throw new ArgumentException(msg);
}
// Else copy elements from skip list into array.
else
{
// Start at the beginning of the skip list.
SkipListNode curr = nillNode.forward[0];
// While we haven't reached the end of the skip list.
while (curr != nillNode)
{
// Copy current value into array.
array.SetValue(curr.entry.Value, index);
// Move forward in the skip list and array.
curr = curr.forward[0];
index++;
}
}
}
protected SkipListNode <T>[] BuildUpdateList(T value)
{
SkipListNode <T>[] updates = new SkipListNode <T> [this.Height];
SkipListNode <T> current = this.Head;
for (int i = this.Height - 1; i >= 0; i--)
{
while (current[i] != null && current[i].Value.CompareTo(value) < 0)
{
current = current[i];
}
updates[i] = current;
}
return(updates);
}
/// <summary>
/// Sets the enumerator to its initial position, which is before
/// the first element in the skip list.
/// </summary>
public void Reset()
{
// Make sure the skip list hasn't been modified since the
// enumerator was created.
if (version == list.version)
{
current = list.nillNode;
moveResult = true;
}
// Else this version of the enumerator doesn't match that of
// the skip list. The skip list has been modified since the
// creation of the enumerator.
else
{
string msg = list.resManager.GetString("InvalidEnum");
throw new InvalidOperationException(msg);
}
}
/// <summary>
/// Adds an element with the provided key and value to the SkipList.
/// </summary>
/// <param name="key">
/// The Object to use as the key of the element to add.
/// </param>
/// <param name="value">
/// The Object to use as the value of the element to add.
/// </param>
public void Add(object key, object value)
{
SkipListNode[] update = new SkipListNode[MaxLevel];
// If key does not already exist in the skip list.
if (!Search(key, update))
{
// Inseart key/value pair into the skip list.
Insert(key, value, update);
}
// Else throw an exception. The IDictionary Add method throws an
// exception if an attempt is made to add a key that already
// exists in the skip list.
else
{
string msg = resManager.GetString("KeyExistsAdd");
throw new ArgumentException(msg);
}
}
/// <summary>
/// Search for the specified key using a comparer.
/// </summary>
/// <param name="key">
/// The key to search for.
/// </param>
/// <param name="curr">
/// A SkipList node to hold the results of the search.
/// </param>
/// <param name="update">
/// An array of nodes holding references to the places in the SkipList
/// search in which the search dropped down one level.
/// </param>
/// <returns>
/// Returns true if the specified key is in the SkipList.
/// </returns>
private bool SearchWithComparer(object key, out SkipListNode curr,
SkipListNode[] update)
{
bool found = false;
// Start from the beginning of the skip list.
curr = nillNode;
// Work our way down from the top of the skip list to the bottom.
for (int i = listLevel - 1; i >= 0; i--)
{
// While we haven't reached the end of the skip list and the
// current key is less than the new key.
while (curr.forward[i] != nillNode &&
comparer.Compare(curr.forward[i].entry.Key, key) < 0)
{
// Move forward in the skip list.
curr = curr.forward[i];
}
// Keep track of each node where we move down a level. This
// will be used later to rearrange node references when
// inserting a new element.
update[i] = curr;
}
// Move ahead in the skip list. If the new key doesn't already
// exist in the skip list, this should put us at either the end of
// the skip list or at a node with a key greater than the sarch key.
// If the new key already exists in the skip list, this should put
// us at a node with a key equal to the search key.
curr = curr.forward[0];
// If we haven't reached the end of the skip list and the
// current key is equal to the search key.
if (curr != nillNode && comparer.Compare(key, curr.entry.Key) == 0)
{
// Indicate that we've found the search key.
found = true;
}
return(found);
}
/// <summary>
/// Inserts a key/value pair into the SkipList.
/// </summary>
/// <param name="key">
/// The key to insert into the SkipList.
/// </param>
/// <param name="val">
/// The value to insert into the SkipList.
/// </param>
/// <param name="update">
/// An array of nodes holding references to places in the SkipList in
/// which the search for the place to insert the new key/value pair
/// dropped down one level.
/// </param>
private void Insert(object key, object val, SkipListNode[] update)
{
// Get the level for the new node.
int newLevel = GetNewLevel();
// If the level for the new node is greater than the skip list
// level.
if (newLevel > listLevel)
{
// Make sure our update references above the current skip list
// level point to the header.
for (int i = listLevel; i < newLevel; i++)
{
update[i] = nillNode;
}
// The current skip list level is now the new node level.
listLevel = newLevel;
}
// Create the new node.
SkipListNode newNode = new SkipListNode(newLevel, key, val);
// Insert the new node into the skip list.
for (int i = 0; i < newLevel; i++)
{
// The new node forward references are initialized to point to
// our update forward references which point to nodes further
// along in the skip list.
newNode.forward[i] = update[i].forward[i];
// Take our update forward references and point them towards
// the new node.
update[i].forward[i] = newNode;
}
// Keep track of the number of nodes in the skip list.
count++;
// Indicate that the skip list has changed.
version++;
}
/// <summary>
/// Removes all elements from the SkipList.
/// </summary>
public void Clear()
{
// Start at the beginning of the skip list.
SkipListNode curr = nillNode.forward[0];
SkipListNode prev;
// While we haven't reached the end of the skip list.
while (curr != nillNode)
{
// Keep track of the previous node.
prev = curr;
// Move forward in the skip list.
curr = curr.forward[0];
// Dispose of the previous node.
prev.Dispose();
}
// Initialize skip list and indicate that it has been changed.
Initialize();
version++;
}
/// <summary>
/// Searches for the specified key.
/// </summary>
/// <param name="key">
/// The key to search for.
/// </param>
/// <param name="curr">
/// A SkipList node to hold the results of the search.
/// </param>
/// <param name="update">
/// An array of nodes holding references to the places in the SkipList
/// search in which the search dropped down one level.
/// </param>
/// <returns>
/// Returns true if the specified key is in the SkipList.
/// </returns>
private bool Search(object key, out SkipListNode curr, SkipListNode[] update)
{
// Make sure key isn't null.
if (key == null)
{
string msg = resManager.GetString("NullKey");
throw new ArgumentNullException(msg);
}
bool result;
// Check to see if we will search with a comparer.
if (comparer != null)
{
result = SearchWithComparer(key, out curr, update);
}
// Else we're using the IComparable interface.
else
{
result = SearchWithComparable(key, out curr, update);
}
return(result);
}
public SkipListEnumerator(SkipList list)
{
this.list = list;
this.version = list.version;
this.current = list.nillNode;
}
