public SkipList(int maxLevels = MAX_LEVELS)
{
_maxLevels = maxLevels >= 1 && maxLevels <= MAX_LEVELS ? maxLevels : MAX_LEVELS;
_head = new Node(int.MinValue + 1, maxLevels);
_head.LevelNodes[0] = new LevelNode(_head);
_random = new Random();
_currentMaxLevels = 0;
}
public void Insert(int value)
{
var map = new Dictionary<int, int> { { 1, 1 }, { 2, 2 }, { 7, 1 }, { 9, 2 }, { 10, 3 } };
// logN operation
int nodeLevels = generateRandomLevelCount(); //map[value];
// avoid going beyond the current max levels
if (nodeLevels > _currentMaxLevels)
{
_head.LevelNodes[_currentMaxLevels] = new LevelNode(_head);
// increase the current max level
_currentMaxLevels++;
nodeLevels = _currentMaxLevels;
}
var node = new Node(value, nodeLevels);
// start scanning from the highest level accessible to this node
// need to update later on the skipped nodes for each level
// and the next for each node on each level
// we cannot do that unless we know how many level 0 nodes were actually skipped
var skippedNodesMap = new Dictionary<int, dynamic>();
var countSkippedPerLevel = new int[_currentMaxLevels];
LevelNode pointer = _head.LevelNodes[_currentMaxLevels - 1];
for (var level = _currentMaxLevels - 1; level >= 0; level--)
{
pointer = pointer.ParentNode.LevelNodes[level];
countSkippedPerLevel[level] = 0;
while (pointer.Next != null)
{
if (pointer.Next.Value > value)
{
// no need to step away, found our node
break;
}
pointer = pointer.Next;
// if we are on the highest level and moving, it means we haven't found the anchor point
if (level != _currentMaxLevels - 1)
{
countSkippedPerLevel[level] += pointer.SkippedNodes + 1;
}
}
if (level < nodeLevels)
{
// create node if needed
var levelNode = new LevelNode(node);
levelNode.Next = pointer.Next;
node.LevelNodes[level] = levelNode;
pointer.Next = levelNode;
// will have to update the skipped nodes for this node
skippedNodesMap[level] = new {
IsNew = true,
Node = levelNode
};
if (level > 0)
{
// we'll update this value later
levelNode.SkippedNodes = 0;
}
else
{
// update values for upper levels
for (int i = 1; i < _currentMaxLevels; i++)
{
dynamic toUpdate = skippedNodesMap[i];
LevelNode nodeToUpdate = toUpdate.Node;
if (toUpdate.IsNew)
{
nodeToUpdate.SkippedNodes = nodeToUpdate.ParentNode.LevelNodes[i - 1].SkippedNodes +
countSkippedPerLevel[i - 1];
if (nodeToUpdate.Next != null)
{
nodeToUpdate.Next.SkippedNodes = nodeToUpdate.Next.SkippedNodes -
nodeToUpdate.SkippedNodes;
}
}
else
{
if (nodeToUpdate.Next != null)
{
nodeToUpdate.Next.SkippedNodes += 1;
}
}
}
}
}
else
{
skippedNodesMap[level] = new
{
IsNew = false,
Node = pointer
};
}
}
}
