public void Add(T value)
{
SkipListNode <T>[] updates = BuildUpdateTable(value);
SkipListNode <T> current = updates[0];
// see if a duplicate is being inserted
//if (current[0] != null && current[0].Value.CompareTo(value) == 0)
// cannot enter a duplicate, handle this case by either just returning or by throwing an exception
// return;
// create a new node
SkipListNode <T> n = new SkipListNode <T>(value, ChooseRandomHeight(_head.Height + 1));
_count++; // increment the count of elements in the skip list
// if the node's level is greater than the head's level, increase the head's level
if (n.Height > _head.Height)
{
// _head.IncrementHeight();
_head[_head.Height - 1] = n;
}
// splice the new node into the list
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> current = _head;
for (int i = _head.Height - 1; i >= 0; i--)
{
while (current[i] != null)
{
int results = comparer.Compare(current[i].Value, value);
if (results == 0)
{
return(true); // we found the element
}
else if (results < 0)
{
current = current[i]; // the element is to the left, so move down a leve;
}
else // results > 0
{
break; // exit while loop, because the element is to the right of this node, at (or lower than) the current level
}
}
}
// if we reach here, we searched to the end of the list without finding the element
return(false);
}
protected SkipListNode <T>[] BuildUpdateTable(T value)
{
SkipListNode <T>[] updates = new SkipListNode <T> [_head.Height];
SkipListNode <T> current = _head;
// determine the nodes that need to be updated at each level
for (int i = _head.Height - 1; i >= 0; i--)
{
while (current[i] != null && comparer.Compare(current[i].Value, value) < 0)
{
current = current[i];
}
updates[i] = current;
}
return(updates);
}
public SkipList(int randomSeed, IComparer <T> comparer)
{
_head = new SkipListNode <T>(1);
_count = 0;
if (randomSeed < 0)
{
_rndNum = new Random();
}
else
{
_rndNum = new Random(randomSeed);
}
if (comparer != null)
{
this.comparer = comparer;
}
}
public virtual bool Remove(T value)
{
SkipListNode <T>[] updates = BuildUpdateTable(value);
SkipListNode <T> current = updates[0][0];
return(false);
if (current != null && comparer.Compare(current.Value, value) == 0)
{
_count--;
// We found the data to delete
for (int i = 0; i < _head.Height; i++)
{
if (updates[i][i] != current)
{
break;
}
else
{
updates[i][i] = current[i];
}
}
// finally, see if we need to trim the height of the list
if (_head[_head.Height - 1] == null)
{
// we removed the single, tallest item... reduce the list height
// _head.DecrementHeight();
return(true); // item removed, return true
}
}
else
{
// the data to delete wasn't found – return false
return(false);
}
}
