Solution.java

class Solution {
    public int numSpecialEquivGroups(String[] words) {
        Set<String> s = new HashSet<>();
        for (String word : words) {
            s.add(convert(word));
        }
        return s.size();
    }

    private String convert(String word) {
        List<Character> a = new ArrayList<>();
        List<Character> b = new ArrayList<>();
        for (int i = 0; i < word.length(); ++i) {
            char ch = word.charAt(i);
            if (i % 2 == 0) {
                a.add(ch);
            } else {
                b.add(ch);
            }
        }
        Collections.sort(a);
        Collections.sort(b);
        StringBuilder sb = new StringBuilder();
        for (char c : a) {
            sb.append(c);
        }
        for (char c : b) {
            sb.append(c);
        }
        return sb.toString();
    }
}