/// <summary>
/// Returns the minimal number of selection which intersection will only match all words with the given string
/// at the given position. If no selection could be made, an empty list will be returned.
/// </summary>
/// <param name="position"></param>
/// <param name="value"></param>
/// <returns></returns>
public ICollection <Selection <int> > GetSelections(int position, SubString value)
{
if (Options.MaxDepth <= 0)
{
return(Array.Empty <Selection <int> >());
}
if (position < 0 || position + value.Length > roots.Length)
{
return(ListWithEmptySelection);
}
var nodes = new List <TrieNode>(value.Length / Options.MaxDepth + 2);
/*
* Separate the string into segments where each segment will correspond to a node.
*
* i.g. with MaxSubStringLength = 3: mes | sag | e
*/
// TODO: This splitting method is not optimal when we only use the minimal selection
int i = 0;
while (i < value.Length)
{
var node = GetNode(position + i, value.ToSubString(i));
if (node == null)
{
return(ListWithEmptySelection);
}
nodes.Add(node);
i += node.Path.Length;
}
/*
* If the last segment is smaller than MaxSubStringLength, its selection might be greater than necessary.
* (see the example above)
* This can be solved by adding character from the previous segment.
*/
if (nodes.Count > 1 && !nodes[nodes.Count - 1].IsLeaf)
{
var lastNode = nodes[nodes.Count - 1];
i = value.Length - lastNode.Path.Length;
while (--i >= 0)
{
var n = GetNode(position + i, value.ToSubString(i));
if (i + n.Path.Length < value.Length)
{
break;
}
lastNode = n;
}
nodes[nodes.Count - 1] = lastNode;
}
// sort by ascending selection size
nodes.Sort((a, b) => a.Selection.Count - b.Selection.Count);
return(nodes.Select(n => n.Selection).ToList());
}