/// <summary>
/// Find the longest word made up of other words
///
/// 'cat', 'cats', 'catsdogcats', 'catxdogcatsrat', 'dog', 'dogcatsdog', 'hippopotamuses', 'rat', 'ratcat', 'ratcatdog', 'ratcatdogcat'
/// Then the longest compound word is ‘ratcatdogcat’ with 12 letters
/// Note that the longest individual words are ‘catxdogcatsrat’ and ‘hippopotamuses’ with 14 letters, but they’re not fully constructed by other words
/// </summary>
/// <param name="text"></param>
/// <returns></returns>
public static string LongestCompoundWord(string[] text)
{
Trie trie = new Trie();
//Add all words in the trie
for (int index = 0; index < text.Length; index++)
{
string word = text[index];
trie[word].Add(index);
}
//for each word, iterate through the trie and find prefixes made up of full word (termininal is true).
//If prefix exists, then it's a possible candidate just search the trie for the remainder of the word
string longestWord = string.Empty;
foreach (string word in text)
{
List<string> segments = new List<string>();
StringBuilder currentWord = new StringBuilder();
TrieNode current = trie.Root;
foreach (char letter in word)
{
current = current.Children[letter];
currentWord.Append(letter);
//we have found an existing word
if (current.IsTerminal)
{
segments.Add(currentWord.ToString());
currentWord.Clear();
}
}
//more than 1 segment
if (segments.Count > 1)
{
//check if remainder is an existing word
if (trie.Contains(segments[segments.Count - 1]))
{
//valid word, check length
if (word.Length > longestWord.Length)
{
longestWord = word;
}
}
}
}
return longestWord;
}
/// <summary>
/// Return all indexes of the search word occurring in the text
///
/// We can parse the text and store all indexes in a dictionary...requires n space and o(1) search time
///
/// Instead of we use more space efficient trie
///
/// author, authority, and authorize - Hashtable index uses 6+9+9=24 characters but trie uses only 6+3+2=11
///
/// </summary>
/// <param name="text"></param>
/// <param name="search"></param>
/// <returns></returns>
public static int[] SearchWordPosition(string[] text, string search)
{
Trie trie = new Trie();
for (int index = 0; index < text.Length; index++)
{
string word = text[index];
trie[word].Add(index);
}
return trie[search].ToArray();
}
