CODE

public class PrefixTree {
  List<List<char>> prefixTree = new List<List<char>>();


  public PrefixTree() {
    
  }
  
  public void Insert(string word) {
    List<char> w = new List<char>();    
    foreach (var c in word)
      w.Add(c);
    prefixTree.Add(w);
  }
  
  public bool Search(string word) {
    foreach (var w in prefixTree)
    {
      if (w[0] != word[0])
        continue;
      int m = 0;
      for (int i = 0; i < w.Count; i++)
      {
        if (i > word.Length-1)
          break;
        if (w[i] != word[i])
          break;
        m++;
      }
      if (m == w.Count)
        return true;
    }
    return false;
  }
  
  public bool StartsWith(string prefix) {      
    foreach (var w in prefixTree)
    {
      if (w[0] != prefix[0])
        continue;
      int m = 0;
      for (int i = 0; i < w.Count; i++)
      {
        if (i > prefix.Length-1)
          break;
        if (w[i] != prefix[i])
          break;
        m++;
      }
      if (m == prefix.Length)
        return true;
    }
    return false;
  }
}