HashSet<String> set = new HashSet<>();
    set.add(words[0]);

    for(int i=1; i<words.length; i++){

        System.out.println("set : " + set);

        word1 = words[i-1].toCharArray();
        word2 = words[i].toCharArray();
        System.out.println("word1, word2 : " + words[i-1] + words[i]);

        if(word1[word1.length-1] == word2[0]){
            if(set.contains(word2)){
                System.out.println("contains");
                answer[0] = i - (n*(int)(i/n)) + 1;
                answer[1] = (int)(i/n) + 1;
                break;
            }else{
                set.add(words[i]);
            }
        }else{
            answer[0] = i - (n*(int)(i/n)) + 1;
            answer[1] = (int)(i/n) + 1;
            break;
        }
    }

    return answer;
}