/// <summary>
/// Adds a new child to this node.
/// </summary>
/// <param name="c">Next character in the prefix</param>
/// <returns>The new node</returns>
public PrefixTreeNode AddChild(char c)
{
var newNode = new PrefixTreeNode(c);
Children[c] = 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(PrefixTreeNode 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>
/// 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 PrefixTreeNode FindNodeRecursive(PrefixTreeNode currentNode, string prefix)
{
if (string.IsNullOrEmpty(prefix))
{
return(currentNode);
}
char nextChar = prefix[0];
if (currentNode.Children.ContainsKey(nextChar))
{
return(FindNodeRecursive(currentNode.Children[nextChar], prefix.Substring(1)));
}
else
{
return(null);
}
}
/// <summary>
/// Recursive function for adding new terms to the tree.
/// Steps through the tree character by character, creating new nodes if needed.
/// When the appropriate leaf node is reached, sets its value to postingListId.
/// </summary>
/// <param name="currentNode"></param>
/// <param name="prefix"></param>
/// <param name="postingListId"></param>
private void AddRecursive(PrefixTreeNode currentNode, string prefix, int postingListId)
{
if (string.IsNullOrEmpty(prefix)) // We have reached the leaf node
{
currentNode.PostingListId = postingListId;
return;
}
char nextChar = prefix[0];
if (currentNode.Children.ContainsKey(nextChar))
{
AddRecursive(currentNode.Children[nextChar], prefix.Substring(1), postingListId);
}
else
{
AddRecursive(currentNode.AddChild(nextChar), prefix.Substring(1), postingListId);
}
}
