/// <summary>
/// Adds a new child to this node.
/// </summary>
/// <param name="str">Next bit of the full prefix</param>
/// <returns>The new node</returns>
public CompactPrefixTreeNode AddChild(string str)
{
var newNode = new CompactPrefixTreeNode(str);
Children[str[0]] = newNode;
return(newNode);
}
/// <summary>
/// Recursively finds the node that has the exact prefix that's given.
/// </summary>
/// <param name="currentNode"></param>
/// <param name="prefix"></param>
/// <returns>Node with the exact prefix or null if such a node doesn't exist.</returns>
private CompactPrefixTreeNode FindNodeRecursive(CompactPrefixTreeNode currentNode, string prefix)
{
var sharedPrefix = SharedPrefix(prefix, currentNode.Prefix);
var uniquePrefix = prefix.Substring(sharedPrefix.Length);
var uniquePrefixFromCurrentNode = currentNode.Prefix.Substring(sharedPrefix.Length);
// Current node's prefix contains all of the search prefix, so this node and all its children have the prefoix
if (string.IsNullOrEmpty(uniquePrefix))
{
return(currentNode);
}
// Current node's prefix and search prefix both differ, so there is no node with the exact prefix we are looking for.
if (!string.IsNullOrEmpty(uniquePrefixFromCurrentNode))
{
return(null);
}
char nextChar = uniquePrefix[0];
if (currentNode.Children.ContainsKey(nextChar))
{
return(FindNodeRecursive(currentNode.Children[nextChar], uniquePrefix));
}
else
{
return(null);
}
}
public CompactPrefixTreeNode Split(int indexInPrefix)
{
var prefixFirstHalf = Prefix.Substring(0, indexInPrefix);
var prefixOtherHalf = Prefix.Substring(indexInPrefix);
Prefix = prefixFirstHalf;
var newNode = new CompactPrefixTreeNode(prefixOtherHalf);
newNode.PostingListId = PostingListId;
newNode.Children = Children;
PostingListId = null;
Children = new Dictionary <char, CompactPrefixTreeNode>();
Children[prefixOtherHalf[0]] = newNode;
return(newNode);
}
/// <summary>
/// Given a start node, recursively collects all the full terms and their posting list ids contained in the subtree.
/// </summary>
/// <param name="currentNode"></param>
/// <param name="currentPrefix">Used to reconstruct the full term, so that we know which posting list id is for which term.</param>
/// <param name="result">Reference to the list that will contain the result.</param>
private void CollectSubtreeEntriesRecursive(CompactPrefixTreeNode currentNode, string currentPrefix, ref List <PrefixResult> result)
{
if (currentNode.PostingListId.HasValue)
{
result.Add(new PrefixResult
{
Term = currentPrefix,
PostingListId = currentNode.PostingListId.Value
});
}
foreach (var node in currentNode.Children.Values)
{
CollectSubtreeEntriesRecursive(node, currentPrefix + node.Prefix, ref result);
}
}
/// <summary>
/// Recursive function for adding new terms to the tree.
/// Steps through the tree according to the next character of the prefix until .
/// When the appropriate leaf node is reached, sets its value to postingListId.
/// </summary>
/// <param name="currentNode"></param>
/// <param name="prefix"></param>
/// <param name="postingListId">Posting list ID to store in the node</param>
private void AddRecursive(CompactPrefixTreeNode currentNode, string prefix, int postingListId)
{
// We have reached the leaf node since its prefix matches our current prefix
if (prefix == currentNode.Prefix)
{
currentNode.PostingListId = postingListId;
return;
}
var sharedPrefix = SharedPrefix(prefix, currentNode.Prefix);
var remainingPrefix = prefix.Substring(sharedPrefix.Length);
var remainingPrefixFromCurrentNode = currentNode.Prefix.Substring(sharedPrefix.Length);
// The node's prefix contains all of the search prefix,
// so we just need to split it into 2 nodes for more granularity.
if (string.IsNullOrEmpty(remainingPrefix))
{
currentNode.Split(sharedPrefix.Length);
currentNode.PostingListId = postingListId;
return;
}
// The node's prefix does not contain all of the search prefix,
// so we need to look deeper into the tree.
else if (string.IsNullOrEmpty(remainingPrefixFromCurrentNode))
{
char nextChar = remainingPrefix[0];
if (currentNode.Children.ContainsKey(nextChar))
{
AddRecursive(currentNode.Children[nextChar], remainingPrefix, postingListId);
}
else
{
AddRecursive(currentNode.AddChild(remainingPrefix), remainingPrefix, postingListId);
}
}
// The node's prefix and search prefix share the same beginning, but then both have more characters,
// so we split the current node and create a new node to contain the last bit.
else
{
currentNode.Split(sharedPrefix.Length);
AddRecursive(currentNode.AddChild(remainingPrefix), remainingPrefix, postingListId);
}
}
