Unique Substrings With Equal Digit Frequency

给一个string, 求unique的相同字频的子字符串.

这题吧, 我看用rolling hash做能快点, 但是我用的count做的.

class Solution {
    public int equalDigitFrequency(String s) {
        Set<String> set = new HashSet<>();
        int n = s.length();
        for(int i = 0; i < n; i++) {
            int[] count = new int[26];
            for(int j = i; j < n; j++) { 
                count[s.charAt(j) - '0']++;
                if(check(count))
                    set.add(s.substring(i, j + 1));
            }
        }
        return set.size();
    }
    public boolean check(int[] count) { 
        int nn = -1;
        for(int n : count){
            if(n != 0)
            {
                if(nn == -1)
                    nn = n;
                else{
                    if(nn != n)
                        return false;
                }
            }
        }
        return true;
    }
}