Part2.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.LinkedList;
import java.util.SortedSet;
import java.util.TreeSet;

public class Part2 {
	
	/**
   * @param x the number of lines to read in
	 * @param r the reader to read from
	 * @param w the writer to write to
	 * @throws IOException
	 */
	public static void doIt(int x, BufferedReader r, PrintWriter w) 
      throws IOException {
      LinkedList<String> words = new LinkedList<>();
      SortedSet<String> sortedWords = new TreeSet<>();

      String line = r.readLine();
      while(line != null){
        if(x == 1 || x == 0){
          w.println(line);
        }
        else if(words.size() < x-1){
          words.add(line);
          sortedWords.add(line);
        }
        else if(words.size() == x-1){
          words.add(line);
          sortedWords.add(line);
          if(sortedWords.last().equals(line)){
            w.println(line);
          }
          sortedWords.remove(words.getFirst());
          words.removeFirst();
        }
        line = r.readLine();
      }
  }

  /**
   * The driver.  Open a BufferedReader and a PrintWriter, either from System.in
   * and System.out or from filenames specified on the command line, then call doIt.
   * @param args
   */
  public static void main(String[] args) {
    try {
      BufferedReader r;
      PrintWriter w;
      int x;
      if (args.length == 0) {
        x = 3;
        r = new BufferedReader(new InputStreamReader(System.in));
        w = new PrintWriter(System.out);
      } else if( args.length == 1) {
        x = Integer.parseInt(args[0]); 
        r = new BufferedReader(new InputStreamReader(System.in));
        w = new PrintWriter(System.out);
      } else if (args.length == 2) {
        x = Integer.parseInt(args[0]); 
        r = new BufferedReader(new FileReader(args[1]));
        w = new PrintWriter(System.out);				
      } else {
        x = Integer.parseInt(args[0]); 
        r = new BufferedReader(new FileReader(args[1]));
        w = new PrintWriter(new FileWriter(args[2]));
      }
      long start = System.nanoTime();
      doIt(x, r, w);
      w.flush();
      long stop = System.nanoTime();
      System.out.println("Execution time: " + 1e-9 * (stop-start));
    } catch (IOException e) {
      System.err.println(e);
      System.exit(-1);
    }
  }
}