COS126

• Download Ballot-queue.java

/***********************************************************************
 * Name: COS 126 Staff
 * NetID: cos126
 * Precept: P99
 * 
 * Ballot: represent a preferential ballot for RIRV
 * 
 * Dependencies: Queue
 * 
 * Note: there are MANY possible correct solutions! This is just one of them.
 */

public class Ballot {
    
    // instance variable: candidate list, favorite first
    private Queue<String> list;  
    
    // constructor: make preferential ballot, ordered favorite to least
    public Ballot(String[] prefs) {
        list = new Queue<String>();
        // favorite, at start of prefs, is the first one in
        for (int i = 0; i < prefs.length; i++)
            list.enqueue(prefs[i]);   
    }
    
    // give string representation, most favorite in front
    public String toString() {
        // to help avoid extra > at start
        boolean first = true;
        
        // build the answer
        String result = "";
        for (String name : list) {
            if (!first)
                result += " > ";
            else 
                first = false;
            result += name;
        }
        return result;
    }
    
    // which remaining candidate is favorite?
    public String top() {
        // return the first name
        for (String name : list)
            return name;
        
        // line to make compiler happy, since it thinks list might be empty
        return "whatever";
    }
    
    // which remaining candidate is least favorite?
    public String bottom() {
        // find and store the last name, overwriting all others
        String last = "whatever";
        for (String name : list) 
            last = name;

        // only the last one remains        
        return last;
    }
    
    // remove candidate from the ballot
    public void cut(String candidate) {
        Queue<String> newList = new Queue<String>();
        
        // keep everyone, in order, except the one we want to eliminate
        for (String name : list) {
            if (!name.equals(candidate))
                newList.enqueue(name);
        }
        
        // did we actually eliminate someone?
        if (newList.size() == list.size())
            throw new RuntimeException(candidate + " not on list");
        
        // save the changes
        list = newList;
    }
    
    public static void main(String[] args) {
        String[] testPrefs = {"Doug", "Nanxi", "Bebe", "Aleksey"};
        Ballot b = new Ballot(testPrefs);
        System.out.println(b); // toString(): "Doug > Nanxi > Bebe > Aleksey"
        
        System.out.println(b.top()); // gives "Doug"
        System.out.println(b.bottom()); // gives "Aleksey"
        
        b.cut("Doug");
        System.out.println(b); // gives "Nanxi > Bebe > Aleksey"
        System.out.println(b.top()); // "Nanxi" - change from original top()
        
        b.cut("Bebe");
        System.out.println(b); // gives "Nanxi > Aleksey"
        
        b.cut("Bebe"); // throws a RuntimeException
    }
}