Solution.java

class Solution {
    public int equalDigitFrequency(String s) {
        int n = s.length();
        int[][] presum = new int[n + 1][10];
        for (int i = 0; i < n; ++i) {
            ++presum[i + 1][s.charAt(i) - '0'];
            for (int j = 0; j < 10; ++j) {
                presum[i + 1][j] += presum[i][j];
            }
        }
        Set<String> vis = new HashSet<>();
        for (int i = 0; i < n; ++i) {
            for (int j = i; j < n; ++j) {
                if (check(i, j, presum)) {
                    vis.add(s.substring(i, j + 1));
                }
            }
        }
        return vis.size();
    }

    private boolean check(int i, int j, int[][] presum) {
        Set<Integer> v = new HashSet<>();
        for (int k = 0; k < 10; ++k) {
            int cnt = presum[j + 1][k] - presum[i][k];
            if (cnt > 0) {
                v.add(cnt);
            }
            if (v.size() > 1) {
                return false;
            }
        }
        return true;
    }
}