import java.util.*;

class Looper {
    
    static int countHellos( List<String> words ) {
        int hellosSoFar = 0;
        while (!words.isEmpty()) {
            // LOOP INVARIANT : the number of times "hello" occurs 
            // in `words` plus hellosSoFar is the same, each time through loop.
            hellosSoFar += ((words.get(0)).equals("hello") ? 1 : 0);
            words = words.subList(1,words.size());
            }
        return hellosSoFar;
        }

    
    static void testCountHellos() {
        List<String> vocab = new LinkedList<String>();
        vocab.add( 0, "hello" );
        vocab.add( 0, "The apple" ); // Like a mutating version of cons??
        vocab.add( 0, "hello" );
        vocab.add( 0, "aloha" );
        
        System.out.println( "Expect 0, got " + countHellos(new ArrayList<String>()) );
        System.out.println( "Expect 2, got " + countHellos(vocab) );
        }
    
    }