1593. Split a string into the max number of unique substrings

//1593. Split a string into the max number of unique substrings

class Solution {
    public int maxUniqueSplit(String s) {
        return backtrack(0, s, new HashSet<>());
    }

    private int backtrack(int start, String s, HashSet<String> seen) {
        if(start == s.length()) {
            return 0; 
        }

        int maxSplits = 0;
        
        for(int end = start + 1; end <= s.length(); end++) {
            String substring = s.substring(start, end);
            
            if(!seen.contains(substring)) {
                seen.add(substring); 
                maxSplits = Math.max(maxSplits, 1 + backtrack(end, s, seen));
                seen.remove(substring);
            }
        }
        
        return maxSplits;
    }
}