public class Solution {
    public int countUniqueWords(String sentence) {

        Set<String> setPalabras = new HashSet<>();
        String[] palabras = sentence.toLowerCase().split(" ");
        for(int i = 0 ; i < palabras.length ; i++){

            if(!palabras[i].equals("")){
                setPalabras.add(palabras[i]);
            }
        }

        return setPalabras.size() < 1 ? 0 : setPalabras.size();
    }
}