public static string[] GetContexts(string sourceText, string key, int len)
{
int N = sourceText.Length;
SuffixArray suffix = new SuffixArray(sourceText);
List <string> contexts = new List <string>();
for (int i = suffix.Rank(key); i < N && suffix.Select(i).StartsWith(key); i++)
{
int from = Math.Max(0, suffix.Index(i) - len);
int count = Math.Min(N - 1, key.Length + 2 * len);
contexts.Add(sourceText.Substring(from, count));
}
return(contexts.ToArray());
}
