ITI1121 Apirl 2014 question 7 exam

Frequency.java

import java.util.List;
import java.util.LinkedList;
import java.util.Iterator;
import java.util.Random;

class Tuple {
  private final char c;
  private boolean visited;

  public Tuple(char c){
    this.c = c;
    visited = false;
  }
  public void toggle() { visited = !visited; }
  public boolean visited() { return visited; }
  public char getChar() { return c; }
  public String toString() {
    if(visited)
      return "("+c+",t)";
    return "("+c+",f)";
  }
}

public class Frequency {
  public static void frequency(List<Tuple> l ){
    while(true){
      final Iterator<Tuple> iter = l.iterator();
      char c     = 0;
      int  count = 0;
      while(iter.hasNext()){
        final Tuple e = iter.next();
        if(e.visited())
          continue;
        if(c==0)
          c = e.getChar();
        else if (c != e.getChar())
          continue;
        e.toggle(); // here we know c == e.getChar()
        count++;
      }
      if(c==0)
        break;
      System.out.print(c + ": "+ count+ "  ");
    }
  }

  private static Random r = new Random(System.currentTimeMillis());
  public static void main(String[] a){
    List<Tuple> l = new LinkedList<Tuple>();
    for(int i=0; i < 10; ++i){
      l.add(new Tuple((char)(r.nextBoolean()?'A':('a'+r.nextInt(26)))));
    }
    System.out.println();
    System.out.println(l);
    System.out.println();
    System.out.println();
    frequency(l);
    System.out.println();
    System.out.println();
    frequency(l);
    System.out.println();
    System.out.println();
    System.out.println(l);
    System.out.println();
    System.out.println();
  }
}