public class WordCount {

  // remember: can compare words alphabetically using str1.compareTo(str2), which returns -1, 0, or 1
  
  public class LineReader {

    // returns whether there's another line
    public boolean hasNextLine() { ... }

    // return the words in the next line 
    public String[] nextLineWords() { ... }

  }

  public class Record {

    // a record with no occurrences
    public Record(String word) { ... }

    // get the word corresponding to this record
    public String getWord() { ... }

    // add another occurrence on the given line
    public void increment(int lineNum) { ... }

    // e.g., "peter.............4: 1 2 3"
    public String toString() { ... }

  }

  public class TreeNode {

    // TODO: TreeNode fields

    // TODO: TreeNode constructor

    // insert a word on the given line into the tree
    public void insert(String word, int lineNum) {
      // TODO
    }

    // build and return the final output of alphabetized records
    public String getFrequencyList() {
      // TODO
    }

  }

  // construct the tree, return the alphabetized list
  public static String buildFrequencyList(LineReader reader) {
    // TODO
  }

}