String-3 > countYZ


            public int countYZ(String str) {
                int words = 0;
                
                for(int i = 0; i < str.length(); i++) {
              
                  if(
                      //put end-checker first so that it'll short-circuit if we're at the end and not try to get an undefined character for the space
                      (i + 1 == str.length() || !Character.isLetter(str.charAt(i+1))) && 
                      (str.toLowerCase().charAt(i) == 'y' || str.toLowerCase().charAt(i) == 'z')
                    ) {
                      words++;
                    }
                }
                
                return words;
              }